7. Performance and Flight Planning
Explain balanced and unbalanced fields.
A balanced field exists when TODA = EMDA (ASDA) or, in other words, when the end of the clearway is the end of the stopway, and the aircraft achieves the screen height over the end of the runway in all cases. Note: A balanced field may be assumed to exist if that part of the clearway which extends beyond the stopway is ignored; therefore, the lower the takeoff distance available (TODA) or emergency distance available (EMDA), the more balanced is field length. Thus an unbalanced field exists when TODA is greater than EMDA. Note: TORA (runway length) does not feature in balanced field calculations. A balanced field length determines the maximum takeoff weight (MTOW). Another definition used for specific types is: a balanced field exists when a balanced V1 is used, namely, when the V1 used (from a V1 range) gives an equal TORA and stopway distance.
How does VMCG/A vary with center of gravity position?
An aft center of gravity position requires a higher VMCG/A. (See Qs: What is VMCG/A speed? pages 189 and 192; How would you teach a student about VMCG/A? page 192.) The turning moment acts around the center of gravity, and if the center of gravity is in the aft position, the vertical tailplane (rudder) moment arm will be shorter, and therefore, the vertical tailplane turning moment is less for a given airspeed. Thus the aircraft requires a higher minimum control speed (VMCG/A) with an aft center of gravity position. Turning moment = rudder to center of gravity arm × speed (VMCG/A) Conversely, the opposite is true for a forward center of gravity position. A forward center of gravity will have a longer arm, and therefore, the vertical tailplane turning moment is greater for a given speed, and thus the aircraft can have a lower VMCG/A.
What are the main variables (conditions) that affect an aircraft's takeoff and landing performance?
An aircraft's takeoff and landing performance is subject to many variable conditions, including 1. Aircraft weight 2. Aircraft flap setting 3. Aerodrome pressure altitude 4. Air density/density altitude (temperature and pressure altitude) 5. Humidity 6. Wind 7. Runway length, slope, and surface (including wet or icy conditions)
How does humidity affect takeoff performance?
High humidity decreases air density, which decreases an aircraft's aerodynamic (CL) and engine performance and results in an increased TOR/D required for a given aircraft weight. (See Q: How does density altitude affect the takeoff performance? page 198.) Therefore, hot, high, and humid mean a decrease in performance that results in either a greater TODR or a lower TOW.
What can you do if an aircraft is limited by a close-in obstacle in the second departure profile segment?
If an aircraft is limited by an obstacle in the second segment because its climb performance is insufficient to clear the obstacle(s), then either of the following flight procedures or a combination thereof can be used to improve the aircraft's climb gradient and thus clear the close-in obstacle(s): 1. Increase takeoff flaps (remaining in the takeoff flap range) 2. Reduce takeoff weight to a level that achieves the required climb gradient that clears the obstacles 3. Increased V2 climb, maintaining takeoff weight 4. Maximum angle climb profile
What does it mean if a takeoff weight is limited by an obstacle in the second segment?
If an aircraft is said to be takeoff-weight-limited by an obstacle in the second segment, this means that the aircraft's takeoff weight has to be reduced to ensure an adequate climb performance at a normal V2 speed to clear any obstacles below the second- to third-segment level-off height.
What can you do if an aircraft is limited by a distant obstacle in the third departure profile segment?
If an obstacle in the third segment limits an aircraft because the obstacle in question is higher than the second- to third-segment level-off height, then either of the following flight procedures or a combination thereof can be used to clear the distant obstacle(s): 1. Extended V2 climb profile technique (See Q: What is an extended V2 climb? page 207.) 2. Reduce takeoff weight to a level that achieves the required climb profile and clears the obstacle 3. Flight path climbing turns to avoid the obstacles Note: The distance and height of the obstacle dictate the procedures available. However, these vary with different aircraft types because of different performance capabilities
What do you do if V1 is greater than VMBE?
If the V1 speed exceeds the maximum brake energy speed (VMBE), then the aircraft's takeoff weight has to be reduced until the V1 speed is less than or equal to VMBE to ensure that the aircraft does not exceed its brake energy limit. (See Q: Describe brake energy limits, page 203.) Hence VMBE can limit V1 and thus MTOW, especially on downward-sloping runways with a tailwind. An aircraft will have a set weight reduction for each knot of speed. Note: VR and V2 need to be redetermined for the lower aircraft weight.
How does weight affect the V1 speed?
If the field length is limiting, the greater the aircraft weight, the lower is the V1 speed. This means that the lower V1 speed provides a greater stopping distance while ensuring that V1 remains greater than VMCG and VMU. If the field length is not limiting, the greater the aircraft weight, the higher is the V1 speed, providing V1 remains less than the VMBE speed and the field length emergency stopping distance is not compromised.
What is the critical point?
"The critical point, or equal-time point, is the en route track position where it is as quick (time) to go to your destination as it is to turn back. The critical point (CP) is calculated as a distance and time from the departure airfield using the following formula: where D is total sector distance, H is ground speed home, and O is ground speed out. Time to CP = distance to CP/O Note: A critical point for an engine-out scenario is different from the all-engine operating critical point and usually is used to determine a worst-case scenario.
How does aircraft weight affect takeoff performance?
Increased aircraft weight results in a greater takeoff distance required (TODR) and a reduced net takeoff climb gradient.
What is island holding fuel, and when is it used?
Island holding fuel is a quantity of fuel uplifted usually in place of diversion fuel that allows an aircraft to hold over a destination aerodrome for an extended period of time. It is often associated with sorties to remote islands, e.g., Easter Island, where there is no diversion option and there is a possibility of a delayed landing due to adverse weather patterns.
How are reverse thrust, antiskid, and braking applied to stopping distance?
Reverse thrust. In general, the performance gained by using reverse thrust is not applied to takeoff emergency stopping distance (EMDR) or landing stopping distance, although a 10 percent safety factor is commonly applied to landing distance in the event of an inoperative thrust reverser. Antiskid. The performance gained by using the antiskid system is applied to both takeoff distance and landing stopping distance. If the antiskid system is inoperative, then takeoff from a wet runway is normally prohibited, and the landing calculation has a large safety factor calculated to its landing distance required, usually about 50 percent. Braking. Maximum braking performance is applied to both takeoff emergency stopping distance (EMDR) and landing distance required.
What is the significance of the 40- to 100-knot call during the takeoff roll?
The 40- to 100-knot call during the takeoff roll is used to check the requirements that need to be established by the called speed. These requirements include 1. Directional control surface (vertical tailplane) starts to become effective with all engines operating. 2. Takeoff engine pressure ratio (EPR) should be set by this check speed so that the pilot is not chasing engine needles for a prolonged period during the takeoff roll. 3. Cross-check the airspeed indicator gauges to ensure their accuracy and reliability. In addition, type-specific requirements also might need to be established by the takeoff roll check speed.
What is the purpose of using balanced field calculations?
The purpose of using a balanced field calculation is to optimize the V2 climb performance (second segment) with a correct V1/VR speed from a single performance calculation/chart without having to perform a second and separate increased V2 calculation and then readjusting the VR calculation.
What is V1 speed?
V1 is the decision speed in the event of an engine failure during the takeoff roll, at which it is possible to continue the takeoff and achieve the screen height (see Q: What is screen height? page 186) within the normal takeoff distance available or to bring the aircraft to a full stop within the emergency distance available (accelerate stop distance). The takeoff must be abandoned with an engine failure below V1, and the takeoff must be continued with an engine failure above V1. Note: If the TOW is limited by TODA, TORA, or EMDA, the V1 speed relates to a single point along the runway where the pilot will have the decision to continue or abort the takeoff in the event of an engine failure. V1 cannot be less than VMCG; V1 cannot be greater than VR or VMBE.
What is the relationship between VS and V2?
V2 is equal to or greater than 1.2 × VS.
What is V3 speed?
V3 speed is the all-engine-operating takeoff climb speed the aircraft will achieve at the screen height.
What is V4 speed?
V4 speed is the all-engine-operating takeoff climb speed the aircraft will achieve by 400 ft, and is used as the lowest height where acceleration to flap retraction speed is initiated.
What is VDF/MDF speed?
VDF/MDF (IAS velocity/Mach) is the maximum flight diving speed for a jet aircraft. It is established as the highest demonstrated speed during flight certification trials.
What is VMCA speed?
VMCA is the minimum control speed in the air for a multiengine aircraft in the takeoff and climb-out configuration, at and above which it is possible to maintain directional control of the aircraft around the normal/vertical axis by use of the rudder within defined limits after the failure of an off-center engine.
What is the difference between VMCA and V2?
VMCA must be less than V2. Normally, V2 is equal to or greater than 1.1 × VMCA. VMCA relates to the airborne directional control of the aircraft in the event of an off-center engine failure. V2 relates to the directional control and a minimum climb performance of the aircraft in the event of an engine failure.
What is the relationship between VMCG and V1?
VMCG has to be equal to or less than V1, thus ensuring that the aircraft can maintain directional control with an off-center engine failure at or above V1, when the aircraft is committed to the takeoff and directional control of the aircraft is essential for safe operation.
What is VMCG speed?
VMCG is the minimum control speed on the ground for a multiengine aircraft at a constant power setting and configuration, at and above which it is possible to maintain directional control of the aircraft around the normal/vertical axis by use of the rudder to maintain runway heading, i.e., on the runway centerline, after the failure of an off-center engine.
What is VMO/MMO speed?
VMO/MMO (IAS velocity/Mach) is the maximum operating speed permitted for all operations. It is normally associated with jet aircraft.
What is VNE speed?
VNE (IAS velocity) is the never-exceed velocity. It is associated with propeller-driven aircraft and is a higher speed than the VNO speed, which can be used when operationally desired but must never be exceeded.
What is VNO speed?
VNO (IAS velocity) is the normal operating speed permitted for all normal operations. It is normally associated with propeller aircraft.
What is the relationship of V1 and VR?
VR is either greater or equal to V1 but never less than V1.
What is VRA/MRA speed?
VRA/MRA is an airspeed for rough air conditions, or turbulence penetration speed. The rough airspeed is recommended for flight in turbulence that is based on the aircraft's VB speed (design speed for maximum gust intensity). It provides speed protection against the two possibilities that stem from the effects of a disturbance in rough air conditions. In other words, the VRA/MRA speed is high enough to allow an adequate margin between the aircraft stall speed and also low enough to protect against structural damage from a high-speed gust disturbance
What is VS speed?
VS (stall speed) is the speed at which the airflow over the wings will stall. The stall speed varies with aircraft weight and configuration. The stall speed is the reference speed for the other performance speeds, i.e., V2, Vref, etc.
What is a range of V1 speeds?
When the planned takeoff weight (TOW) is not field-length-limited, i.e., not limited by TORR, TODR, or EMDR, there may be a range of V1 speeds; e.g., between 125 and 135 knots when the pilot has a stop-go option in the event of an engine failure. The minimum V1 speed in the range is still restricted by the VMCG speed, and the maximum V1 is still restricted by the VMBE. A range allows the V1 speeds to be raised or lowered to achieve a different departure profile or climb technique, i.e., an increased TOW or an increased V2 climb for obstacle clearance. However, normally, a single V1 speed is chosen within the range prior to commencing the takeoff run. Thus, if an engine failure does occur, the decision effectively has already been determined, thus removing any delayed response and indecision that an analysis of a V1 range at the time of the engine failure might precipitate, which improves operational safety.
How does wind affect the takeoff performance?
Wind has a profound effect on the takeoff performance of an aircraft. An aircraft may experience either a headwind, tailwind, or crosswind. (See Q: What are the crosswind limitations on an aircraft? page 200.) Headwind. A headwind reduces the takeoff distance required for a given aircraft weight or permits a higher TOW for the TOR/D available. Thus the greater the headwind, the better is the aircraft performance. Tailwind. A tailwind increases the takeoff distance required for a given aircraft weight or requires a lower TOW for the TOR/D available. Thus the greater the tailwind, the worse is the aircraft performance. It is for this reason that a takeoff with a tailwind shows very poor airmanship.
When are you not permitted to takeoff from a wet runway?
You are not permitted to takeoff from a wet (contaminated) runway when 1. The aircraft antiskid system is inoperative. 2. The standing water level is above a specified limit. 3. Any other type-specific restrictions.
Explain a typical fuel plan for a trip.
A typical fuel profile for a flight would include sufficient fuel for the following: 1. Takeoff and climb at takeoff thrust 2. Climb to the initial cruise altitude at maximum continuous thrust 3. En route cruise, including intermediate step climbs 4. Descent to a diversion point (go-around point) over the destination aerodrome 5. Contingency fuel 6. Diversion to over an alternative aerodrome 7. An instrument approach and landing 8. An additional amount of holding fuel may be required if the destination is an island with no alternative or you are arriving at a major airport at its busiest period, e.g., London Heathrow between 0700 and 0930.
What is climb gradient?
Climb gradient is the ratio, in the same units, expressed as a percentage of change in height divided by horizontal distance traveled. The climb gradients on performance charts are true gradients for the all-up weight (AUW) of the aircraft, which allows for temperature, aerodrome pressure altitude, and aircraft configuration. That is, they are achieved from true rates of climb, not pressure.
What is the typical jet takeoff technique and the various flight path options?
"The takeoff flight path is based on the following technique and options: The flight path begins at reference zero, where the jet aircraft has attained a height of 35 ft (in dry conditions) and V2 after failure of its critical engine at V1. Landing gear retraction is completed at the end of the first segment, and the climb is continued at V2 with takeoff flaps and takeoff thrust on the operating engine(s) until the second- to third-segment level-off transition takes place at either (1) a minimum gross height of 400 ft or (2) the maximum standard gross height, usually 1000 ft. After option 1 or 2, the aircraft is then accelerated in level flight, flaps are retracted, and acceleration is continued to the final segment, where the climb is reassumed on maximum continuous thrust or (3) the maximum height, which can be reached using either (1) takeoff thrust for its maximum period after the brakes are released, usually 5 minutes, or (2) maximum continuous thrust to an unrestricted height Option 3 is used to clear distant obstacles, i.e., in the normal third segment using an extended V2 technique to gain a greater climb gradient. (See Qs[...]
What is V2 speed?
"V2 speed is the takeoff safety speed achieved by the screen height in the event of an engine failure that maintains adequate directional control and climb performance properties of the aircraft. Note: V2 is also known as the takeoff safety speed (TOSS). V2 cannot be less than VS × 1.20 and VMCA × 1.10.
How would you teach a student about VMCG/A?
"VMCG/A relates to the minimal directional (heading) control speed on the ground or in the air, at which the turning moment produced by the vertical tailplane with maximum rudder deflection is sufficient to balance the yawing moment of the aircraft nose when the aircraft loses an off-center engine (asymmetrical power). The heading of an aircraft is determined by the direction of the nose of the aircraft, which is pivoted about the normal/vertical axis at the center of gravity point. With an off-center engine failure, and assuming a constant power and configuration setting, the aircraft will yaw about the center of gravity point to the dead engine due to the asymmetrical thrust properties. This yaw changes the aircraft's direction. The magnitude of the yaw is a function of the asymmetrical thrust × aircraft nose to center of gravity arm. That is, Yawing moment = asymmetrical thrust × nose to center of gravity arm Whenever the aircraft is committed on the takeoff run, i.e., past V1, or in the air, this yawing moment has to be balanced to maintain directional control of the aircraft. The directional control is provided by the aircraft's vertical tailplane and its rudder control surface, which[...]
What is VR speed?
"VR (rotation speed) is the speed at which the pilot initiates rotation during the takeoff to achieve V2 at the screen height, even with an engine failure. VR cannot be less than 1.05 VMCA/1.1 or 1.05 VMU.
What is cost index?
A cost index (CI) is a performance management function that optimizes the aircraft's speed for the minimum cost. Note: Primary goal is to minimize direct operating costs per trip by means of a trade-off between operating costs per hour and incremental fuel burn. The CI is used to take into account this relationship. The CI computes the best economic speed and Mach to be flown, considering the ratio between the flight time costs (or direct operating costs) and the fuel cost. CI 0 = minimum fuel consumption (maximum range) CI 999 = minimum time Cost indices form part of a company's stored route and are inserted into the flight management computer (FMC). They take into account specific route factors such as the price of fuel at the departure and destination airports so that the aircraft is flown at the correct speed to balance the fuel costs against the dry operating costs. An incorrect CI will always cost more money. Cost index optimizes aircraft speed for the minimum costs. It is the ratio of flight time costs (CT) to fuel cost (CF). CI = CT/CF kg/min or 100 lb/hour
What is a cruise (step) climb?
A cruise (step) climb occurs when an aircraft in the cruise loses weight due to fuel burn, which allows the aircraft to fly higher; therefore, a cruise (step) climb is initiated to climb the aircraft to its new maximum altitude. Note: An aircraft may have several step climbs, especially on long-haul routes. A cruise climb is important because a jet aircraft's most efficient performance is gained at its highest possible altitude.
A derated takeoff will use more or less trip fuel, and why.
A derated takeoff uses more trip fuel. This is so because, as with a reduced-power climb, the aircraft has a slower initial rate of ascent and therefore takes longer to reach its transition to its en route climb profile and then its cruise altitude. Consequently, it spends less time at its optimal cruise altitude and therefore uses more trip fuel. Note: Remember that at its optimal cruise altitude an aircraft experiences the best aerodynamic and engine performance, which results in the best fuel economy (SFC).
What is the difference between a dry V1 and wet V1?
A dry (maximum) V1, is the normal decision speed that following an engine failure allows the takeoff to be continued safely within the TODA or to be stopped safely within the EMDA. A wet (minimum) V1 is the maximum speed for abandoning a takeoff on a contaminated runway. A wet V1 improves the stopping capabilities (final stop point) back to the dry conditions level but degrades the takeoff chances with a reduced screen height in the event of a takeoff being continued. A recommended wet V1 for contaminated conditions is the dry V1 - 10 knots. Thus wet V1 is a lower speed than dry V1. The wet V1 is not a V1 speed because it does not imply any ability to continue the takeoff following an engine failure, and unlike a dry V1, this speed may be less VMCG. Therefore, a takeoff from a wet runway may result in a risk period between the maximum speed for abandoning the takeoff (wet V1) and the normal V1 speed, during which, in the event of an engine failure, the speed is too high for a successful stop on a contaminated runway.
What results does a flight carried out below its optimum altitude have on jet performance?
A flight carried out below its optimum altitude uses more fuel but takes less time to complete the trip when flying at a constant Mach number (MN). Note: Optimum altitude is either the aircraft's highest attainable altitude, i.e., service ceiling, which for a jet typically would be an altitude above flight level (FL) 260, and thus the MN speed flown is constant because the MN is the limiting speed, or the most economic FL for a given cost index, weight, wind data, and outside air temperature. It is a compromise between fuel and time saving, namely, slightly higher fuel usage but shorter time than its highest alternate FL. Note: Higher FL means that time increases and fuel consumption decreases (in still air and at a constant MN). Lower FL means that time decreases and fuel consumption increases (in still air and at a constant MN). The aircraft uses more fuel because the engines are designed to achieve their best specific fuel consumption (SFC) at a high operating rpm, which can only be achieved at high (optimum) altitudes. (See Q: Why does a jet aircraft climb as high as possible? page 49.) Therefore, when a flight is carried out below[...]
How does pressure altitude affect takeoff performance?
A high aerodrome elevation (high pressure altitude) decreases an aircraft's performance and results in an increased takeoff distance required (TODR). Therefore, high means a decrease in performance that results in either more takeoff distance required or a lower takeoff weight.
Will a reduced/variable thrust (flex) or derated takeoff use more or less trip fuel, and why?
A reduced/variable thrust or derated takeoff uses more trip fuel. This is because, as with a reduced-power climb, the aircraft has a slower initial rate of ascent and therefore takes longer to reach its transition to its en route climb profile and then its cruise altitude. Consequently, it spends less time at its optimum cruise altitude and therefore uses more trip fuel. Note: Remember that at its optimum cruise altitude, an aircraft experiences the best aerodynamic and engine performance, which results in the best fuel economy (SFC).
How can a stopway extend beyond the clearway?
A stopway sometimes may extend beyond the clearway if the length of the clearway is limited because of an obstruction within 75 m of the runway/stopway centerline. (See Q: What is the runway clearway? page 185.) However, this obstruction does not limit the stopway, which only needs to be as wide as the runway.
What is an assumed/flexible temperature?
An assumed/flexible temperature is a performance calculation technique used to find the takeoff engine pressure ratio (EPR) setting for an aircraft's actual takeoff weight. This is known as a reduced/derated thrust value. First, it should be clearly understood that the full takeoff thrust is calculated against an aircraft's performance limited (either field length, WAT, tire or net flight path, obstacle clearance climb profile) maximum permissible takeoff weight (MTOW), which itself is calculated from the ambient conditions of aerodrome pressure altitude and temperature. However, in many cases, the aircraft takes off with a weight lower than the maximum permissible takeoff weight. When this happens, an assumed temperature performance technique presents a method of calculating a decreased takeoff thrust that is adapted for the aircraft's actual takeoff weight. This is done by calculating the corresponding assumed/flexible temperature (higher than the actual air temperature) from the weight, altitude, and temperature (WAT) performance graph by using the aircraft's actual takeoff weight as if it were the performance-limiting MTOW against the actual aerodrome altitude to find the limiting temperature. Note: Temperature increases as the maximum permissible weight decreases, so it is possible to assume a temperature at which the actual[...]
What is an extended V2 climb?
An extended V2 climb is one in which the aircraft's second-segment climb; i.e., at V2 and takeoff flaps, is either (1) continued to the highest possible level-off height, allowing for acceleration and flap retraction, if applicable, which can be reached with maximum takeoff thrust on all operating engines for its maximum time limit, normally 5 minutes, or (2) continued to an unlimited height with maximum continuous thrust, instead of takeoff thrust, that meets the aircraft's minimum acceleration and climb gradient requirements in the takeoff flight path above 400 ft.
Why is an extended V2 climb used?
An extended V2 climb is used to clear distant third-segment obstacles that are higher than the normal second- to third-segment level-off height, which is typically between 400 and 1000 ft. An extended V2 may only be used to clear the last obstacle in the flight path so that a normal third-segment acceleration and final-segment profile can be achieved.
How does air density (rho)/density altitude (pressure altitude and temperature) affect the takeoff performance?
An increase in density altitude (decrease in air density) increases the takeoff distance required (TODR). Therefore, hot and high mean a decrease in performance that results in either a greater TODR or a lower TOW.
When is an increased V2 climb profile used?
An increased V2 climb profile technique can only be used if the take-off weight is not restricted by field length limits so that some or all of the excess field length can be used to increase takeoff speed VR and thus V2 speed. Increased V2 technique is used for the following reasons: 1. To achieve a greater obstacle clearance performance with an improved takeoff climb gradient without reducing takeoff weight 2. To allow a higher aircraft takeoff weight that achieves the standard (minimum) takeoff climb gradient corresponding to the required obstacle clearance gradient The use of increased V2 techniques usually is prohibited on wet runways.
What is an increased V2?
An increased V2 is a technique for improving an aircraft's climb gradient performance in the second segment by increasing the V2 climb speed. That is, increasing the V2 base speed increases lift because lift is a function of speed, and for a given weight, an increased V2 speed will provide an increase in lift, thus producing a greater net climb gradient. Thus an increased V2 climb allows higher obstacles to be cleared in the second segment climb-out profile. Note: An increased V2 speed requires either a greater than normal takeoff distance (TOD) or a reduced aircraft weight.
What are the following aircraft weight definitions?
Basic weight. The weight of the empty aircraft with all its basic equipment plus a declared quantity of unusable fuel and oil. Note: For turbine-engined aircraft and aircraft not exceeding 5700 kg, the maximum authorized basic weight may include the weight of its usable oil. Variable load. The weight of the crew, crew baggage, and removable units, i.e., catering loads, etc. Variable load = APS - basic weight APS weight. Aircraft prepared for service (APS). APS = basic weight + variable load Payload. Passengers and/or cargo. Disposable load. The weight of the payload and fuel. Disposable load = TOW - APS Ramp weight. Ramp weight (RW) is the gross aircraft weight prior to taxi. Note: RW must be within its structural maximum (certificate of airworthiness) weight limit. RW = TOW + fuel for start and taxi MTOW. Maximum takeoff weight (MTOW) is the maximum gross weight of the aircraft permitted for takeoff. Note: Sometimes a performance-limited MTOW (i.e., short runway, obstacle clearance) may limit the aircraft to a weight less than its structural maximum (certificate of airworthiness) weight. MLW. Maximum landing weight (MLW) is the maximum gross weight of the aircraft permitted for landing. Note: Sometimes a performance-limited MLW (i.e., short runway, obstacle[...]
What is the critical speed?
Critical speed is the lowest possible speed on a multiengine aircraft at a constant power setting and configuration at which the pilot is able to maintain a constant heading after failure of an off-center engine. VMCG/A/L are particular configurations and stage of flight critical speeds.
If you had an engine failure between V1 and VR and you had a maximum crosswind, which engine would be the best to lose, i.e., upwind or downwind engine?
Downwind engine. This is so because the crosswind would then oppose the yawing moment of the upwind engine. (See Q: How does a crosswind affect the critical engine? page 60.) Note: The critical engine failure is the failure of the upwind engine.
What is the emergency distance available (EMDA)/accelerate stop distance available (ASDA)?
Emergency distance available (also known as the accelerate stop distance available, or ASDA) is the length of the takeoff run available, usually the physical length of the runway, plus the length of any stopway available. That is
What is the emergency distance/required (ED/EDR)?
Emergency distance required is the distance required to accelerate during the takeoff run on all engines to the critical speed, V1, at which point an engine failure is assumed to have occurred, and the pilot aborts the takeoff and brings the aircraft to a halt before the end of the runway or stopway if present; i.e., RTO. The whole emergency distance is factored by a safety margin, normally 10 percent. Note: The use of reverse thrust in the EDR calculation differs from authority to authority but usually it is not factored in the EDR calculation. ED is sometimes referred to as an accelerated stop distance. The EDR must not exceed the EMDA.
How does a contaminated runway (ice and rain) affect distance and V1 speed?
For a given aircraft weight on a contaminated runway, the emergency distance required is increased because of a reduced braking ability. Also, a contaminated runway has a slower acceleration, and therefore, the TORR is increased, which limits the stopping distance available if the takeoff is field-length-limited. This effect is normally built into takeoff run performance graphs. If distance is limited, the normal dry V1 offers the best compromise in risk associated with a continued or aborted takeoff. Namely, there is a risk of not being able to stop within the EMDA. However, it is a remote possibility that an engine failure will occur at the worst point, i.e., after the wet V1 and before the dry V1; therefore, an incident in the transition to flight in this scenario is a low risk. Furthermore, even if you lose an engine between the wet and dry V1 speeds, aborting the takeoff probably will only result in a runway overrun at a low speed. If there is a distance to spare, i.e., not field length limited, then a progressive reduction in the V1 speed to the wet V1 reduces the risk associated with the aborted takeoff without unduly compromising the[...]
Explain fuel howgozit?
Fuel howgozit is a comparison of the actual fuel remaining against the planned fuel remaining along the flight path. At any stage of flight an estimate of the fuel difference can be obtained, and it is ideal to show any trends, such as increasing fuel burn. Note: Fuel howgozit charts also can be used to plan the position of the point-of-no-return (PNR) point.
What is Va speed?
Maneuvering speed is the airspeed at which maximum elevator deflection causes the stall to occur at the airframe's load factor limit. Va for maximum aircraft weight is specified in the flight manual.
What is VMBE speed?
Maximum brake energy speed (VMBE) is the maximum speed on the ground from which a stop can be accomplished within the energy capabilities of the brakes.
Describe a maximum-angle (Vx) climb profile.
Maximum- or best-angle climb (Vx) is the steepest angle or highest gradient of climb used to clear close-in obstacles over the shortest horizontal distance.
Describe the minimum-rate (Vy) climb profile.
Maximum- or best-rate climb (Vy) is the highest vertical speed that gains height in the shortest time.
What is the difference between maximum-range cruise (MRC) and long-range-cruise (LRC)?
Maximum-range cruise. This is the speed at which, for a given weight and altitude, the maximum fuel mileage is obtained. It is difficult to establish and maintain stable cruise conditions at maximum-range speeds. Long-range cruise. This is a speed significantly higher than the maximum-range speed, i.e., 10 knots (M 0.01), which results in a 1 percent mileage loss at a constant altitude. The long-range cruise schedule requires a gradual reduction in cruise speed as gross weight decreases with fuel burnoff.
What is the takeoff run available (TORA)?
Takeoff run available (for all engine operations) is the usable length of the runway available that is suitable for the ground run of an aircraft taking off. In most cases this corresponds to the physical length of the runway.
Where are you likely to need a point of no return (PNR)?
PNR calculations are important for aircraft for which diversion airfields are not readily available, e.g., over large water areas such as the Pacific Ocean. It is crucially important to have a PNR point if you elect to carry island holding fuel instead of diversion fuel because you become solely committed to landing at your destination once you pass the PNR point. Note: PNR points are not really required on a route over land with diversion airfields available en route.
What are the recommended adjustments to headwind and tailwind components when calculating the takeoff and landing field length performance?
Not more than 50 percent of the reported headwind or not less than 150 percent of the reported tailwind should be used to calculate the takeoff or landing performance. These adjustments provide a safety margin to the reported wind that covers acceptable fluctuations of the actual wind experienced.
What is the point of no return (PNR)?
PNR (point of no return) is the last point on a route at which it is possible to return to the departure aerodrome with a sensible fuel reserve. Normal PNR points are based on the aircraft's safe endurance. The all-engine PNR formula is where E is the safe endurance time, H is the ground speed home, and O is the ground speed out. Distance to PNR = time to PNR × O The one-engine PNR distance is calculated as follows: 1. Calculate a 1-nautical-mile round-trip fuel flow (all-engine ground speed out and one-engine-inoperative ground speed home) 2. Safe endurance divided by 1-nautical-mile round trip fuel flow One-engine PNR time is calculated by distance divided by ground speed out.
How is range increased when flying into a headwind?
Range can be increased in some circumstances when flying into a headwind, i.e., light headwinds, because the best range speed will be a little faster, and the airspeed represents the rate of distance covered. Therefore, range will be increased with a headwind. The increased fuel flow is compensated for by a higher speed, allowing less time en route for the headwind to act.
If VMCG is limiting for the weight of the aircraft, what can you do?
Reduce takeoff thrust. The vertical tailplane (rudder) turning moment is used to oppose/balance the asymmetrical thrust yawing moment to maintain directional control. Therefore, by reducing thrust, any off-center engine loss during the takeoff run has a reduced asymmetrical thrust imbalance, which thereby reduces the yawing moment experienced and thus requires a reduced tailplane turning moment to maintain directional control. And because the magnitude of the tailplane turning moment is a product of airspeed, a lower (VMCG) ground speed maintains the aircraft's directional control. Thus, reduced takeoff thrust gives rise to a lower VMCG.
What is the takeoff run required (TORR)?
Takeoff run required (for all engine operations) is the measured run (length) required to the unstick speed (VR) plus one-third of the airborne distance between the unstick and the screen height. The whole distance is then factored by a safety margin, usually 15 percent.
How does the runway length, surface, and slope affect takeoff performance?
Runway length. The length of the available runway is one of the performance limitations that restricts the maximum weight of the aircraft. The greater the runway length, the greater is the acceleration the aircraft can gain, and higher is the liftoff speed (VR) the aircraft can obtain. And because the VR speed is related to aircraft weight, it can be seen that the longer the runway available, the greater is the possible aircraft takeoff weight. Note: Other limitations, such as the maximum permissible structural certificate of airworthiness weight of the aircraft may be more limiting than the runway length. Runway surface. A hard and dry runway surface allows good acceleration on the ground and therefore reduces the takeoff run required for a given aircraft weight or allows a higher aircraft weight for a given runway length. On other surfaces, e.g., grass or wet contaminated hard surfaces, the acceleration is retarded on the ground, and therefore, the takeoff run and distance required are increased. Note: Takeoff performance graphs and tables (i.e., field length) normally allow for such variations in surface conditions. Runway slope. A downward slope allows the aircraft to accelerate faster; therefore, the takeoff run and distance required for[...]
How does screen height change with a wet V1?
Screen height is reduced for a jet aircraft using a wet V1. This is due to a portion of the airborne distance being added to the ground run as a result of the increased ground run used between the wet V1 and VR if an engine failure occurs at the worst point, i.e., just after the wet V1 and prior to VR. Note: However, most propeller aircraft have no change in V1 and screen height in wet conditions.
What is screen height?
Screen height relates to the minimum height achieved over the runway before the end of the clearway should an engine failure occur on takeoff. The screen height also marks the end of the takeoff distance.
What is the takeoff distance available (TODA)?
Takeoff distance available (for all engine operations) is the length of the usable runway available plus the length of the clearway available, within which the aircraft initiates a transition to climbing flight and attains a screen height at a speed not less than the takeoff safety speed (TOSS) or V2. TODA = usable runway + clearway TODA is not to exceed 1.5 × TORA (takeoff run available). The TODA/R and TOSS/V2 are the vital performance figures for a pilot during the takeoff.
What is the takeoff distance required (TODR)?
Takeoff distance required (for all engine operations) is the measured distance required to accelerate to the rotation speed (VR) and thereafter effect a transition to a climbing flight and attain a screen height at a speed not less than the takeoff safety speed (TOSS) or V2. The whole distance is factored by a safety margin, usually 15 percent.
What is the absolute ceiling?
The absolute ceiling is an aircraft's maximum attainable altitude/flight level at which the Mach number buffet and prestall buffet occur coincidentally. This scenario is known as coffin corner. (See Q: What is coffin corner? page 26.) Therefore, an aircraft is unable to climb above its absolute ceiling. The absolute ceiling is determined during flight certification trials.
What are the crosswind limitations on an aircraft?
The aircraft must not takeoff or land in a crosswind that exceeds its certified maximum crosswind limitation for the aircraft type to safeguard directly the directional and lateral control and indirectly the takeoff run performance of the aircraft.
What climb departure uses the least trip fuel?
The best rate of climb (Vy) departure uses the least trip fuel because it ensures that the aircraft reaches its optimal cruise altitude as quickly as possible, and therefore, the aircraft spends a greater part of its flight time at its optimal altitude than with any other climb profile. The optimal en route altitude has the best aerodynamic and engine performance qualities. By being at this optimal cruise altitude as long as possible, the best fuel economy and specific fuel consumption (SFC) are obtained for the largest percentage of the flight (trip), and therefore, the least trip fuel is used.
Describe brake energy limits.
The brake energy capacity limits the aircraft's maximum takeoff weight (MTOW) given the ambient aerodrome pressure altitude, temperature, wind, and runway slope conditions so that V1 does not exceed VMBE to ensure that the aircraft's brake system has sufficient energy to dissipate and stop the aircraft's inertia from V1 under most operating conditions.
What is the runway clearway?
The clearway is the length of an obstacle-free area at the end of the runway in the direction of the takeoff, with a minimum dimension of 75 m either side of the extended runway centerline that is under the control of the licensed authority. Note: The clearway surface is not defined and could be water. It is an area over which an aircraft may make a portion of its initial climb to a specified height, i.e., to the screen height, 35 ft.
How does the wind affect the position of the critical point?
The critical point moves into the wind. Given still air conditions, the critical point (CP) between two aerodromes is simply the halfway point. However, the effect of wind displaces the critical point to one side or the other of the midpoint. Flying into a headwind moves the CP closer to the destination aerodrome, and flying with a tailwind moves the CP closer to the departure aerodrome. This is so because the CP is the equal time point to reach an airfield, and therefore, ground speed is all-important, and ground speed is TAS × WV.
Describe the cruise climb profile.
The cruise climb profile is a compromise between the best en route speed profile and the best climb profile—most commonly used by commercial traffic. It provides faster en route performance, a more comfortable aircraft attitude, better aircraft control due to lower angle of attack, and greater airflow over the control surfaces.
Describe the difference between net and gross flight paths/performance.
The difference between the net and gross flight paths/performance is as follows: The gross performance is the average performance that a fleet of aircraft should achieve if maintained satisfactorily and flown in accordance with the techniques established during flight certification and subsequently described in the aircraft performance manual. Gross performance therefore defines a level of performance that any aircraft of the same type has a 50 percent chance of exceeding at any time. The net performance is the gross performance diminished to allow for various contingencies that cannot be accounted for operationally, e.g., variations in piloting technique, temporarily below-average performance, etc. It is improbable that the net performance/flight path will not be achieved in operation, provided the aircraft is flown in accordance with the recommended techniques, i.e., power, attitude, and speed. Normally, performance graphs show net performance; however, some performance charts, especially for three-engined aircraft, assume gross is equal to net performance. This means that no margin exists between what the graph suggests the aircraft will achieve and what the aircraft will achieve.
How does the use of flaps affect the aircraft's takeoff performance?
The effect of flaps on the takeoff performance, i.e., TOR/TOD, and climb performance varies between different aircraft types, especially between swept-wing (jet) and straight-wing (turboprop) aircraft and further with the degree of flap deployed on individual aircraft. Swept-wing (jet) aircraft. Swept-wing aircraft require a low flap setting, i.e., takeoff flap, to improve the CL during the takeoff. This has two positive effects. First, a low flap setting reduces the aircraft's takeoff run required (TORR) because the higher CL lowers the stalling speed (VS), which in turn reduces the V2 and VR speeds and results in the aircraft reaching its liftoff speed from a shorter ground takeoff run (TORR). Second, a low flap setting reduces the aircraft's takeoff distance required (TODR) because the increased CL benefits outweigh the increased airborne drag and thereby improve the climb performance of the aircraft, resulting in the aircraft reaching the screen height over a shorter distance. Maximum takeoff flaps may be used to reduce the ground takeoff run required when the field length is limiting or the runway surface is poor. However, airborne climb performance may be compromised due to an increase in drag, which reduces the lift-drag[...]
What factors determine the loading (weight and balance) of an aircraft?
The factors that determine the loading (weight and balance) of an aircraft are 1. To ensure that the following combined component weights do not exceed the aircraft's overall gross weight limitations, i.e., MTOW, ZFW, structural maximum (certificate of airworthiness) aircraft weight, etc.: a. Cargo b. Baggage c. Crew and passengers, including personal effects (approximate weights can be used) d. Removable equipment e. Fuel (SG weight) 2. The distribution of the weights ensures that the center of gravity is within its limits to longitudinally balance the aircraft. (See Q: Describe center of gravity, page 12.) This is accomplished by adding up the various component moments to obtain the total moment. (See Q: Describe center of gravity moment, page 12.) The various component weights act at known positions relative to the fixed datum (arm). Each of these has a moment, which we can calculate by multiplying the individual weight by its arm from the datum. We obtain the total moment by adding up all the moments of these component weights and then by using the formula we can calculate the center of gravity position. Carrying out the weight and balance/loading calculation for an aircraft is essential for a safe flight.
What is a maximum service ceiling?
The maximum service ceiling is an aircraft's' imposed en route maximum operating altitude/flight level, which provides a safety margin below its absolute ceiling.
What guaranteed altitude/height would you be able to achieve at MTOW WAT-limited conditions with one engine inoperative?
The minimum height an aircraft would be able to achieve given these conditions would be the circuit height, i.e., 1500 ft.
What is the most important diversion question to ask in an emergency?
The most important question to ask in an emergency given two diversion aerodromes is, Which aerodrome is the quickest to get to?
Describe field length limits.
The most restrictive field length available from either 1. The all-engine-operating runway length 2. The runway emergency distance length available, or 3. The one-engine-inoperative runway length limits the aircraft's MTOW (or MLW) so that it meets the required TOR/D performance given the ambient aerodrome conditions of pressure altitude and temperature (density).
Describe the net takeoff flight path (obstacle clearance).
The net takeoff flight path is the true height versus the horizontal distance traveled from reference zero, assuming failure of the critical engine at V1, and it is used to determine the obstacle clearance by a specified minimal amount, normally 35 ft.
What are the normal en route operating performance limitations for an aircraft?
The normal en route operating performance limitations for an aircraft are 1. En route obstacle/terrain clearance with one or two engines inoperative 2. Maximum range limit 3. Extended twin operations (ETOPS) time limit
How high is the screen height for propeller and jet aircraft?
The screen height for propeller-engined aircraft in dry conditions is 50 ft. Note: Most propeller aircraft have an increased accelerate/stop distance in wet conditions but no change in V1 or screen height. The screen height for jet aircraft in dry conditions is 35 ft. Note: Less than propeller aircraft due to the lower CL of the jet aircraft's swept wing. In wet conditions, the jet aircraft's screen height is reduced to a minimum of 15 ft in most cases. This is so because when an engine failure occurs at the worst point, i.e., after V1 (wet or dry) and prior to VR, a proportion of the airborne distance is added to the ground run. (See Q: How does screen height change with a wet V1? page 191.) Note: V2 will only be achieved at 35 ft; therefore, at a reduced screen height of 15 ft the aircraft speed will be less than V2. Thus screen height relates to engine failure scenarios and changes with runway conditions for jet aircraft, i.e., 35 ft for 1 engine inoperative/dry conditions and 15 ft for 1 engine inoperative/wet conditions.
What is the runway stopway?
The stopway is the length of an unprepared surface at the end of the runway in the direction of the takeoff that is capable of supporting an aircraft if the aircraft has to be stopped during a takeoff run.
Define maximum endurance and range with reference to the drag curve.
The total drag generated by an aircraft is high at both high and low airspeeds. At high airspeeds the total drag is high because the aircraft experiences a lot of profile drag, and at low airspeeds the total drag is high because the aircraft experiences a lot of induced drag. Minimum drag occurs at an intermediate speed (VIMD). This is presented by an aircraft's drag curve. (See Qs: What is drag? page 6; Describe the two major types of drag and their speed relationship, page 6; Describe the drag curve on a propeller/jet aircraft, pages 7 and 8.) Maximum endurance. This is achieved by flying at the maximum-endurance airspeed, which is the indicated airspeed that relates to the thrust required to balance the minimum drag (VIMD) experienced by the aircraft. Minimum drag (VIMD) is the lowest point/airspeed on the drag curve. And given that thrust is a product of engine power and fuel consumption is a function of the engine power used, the aircraft thus has the lowest fuel consumption in terms of pounds of fuel used per hour and hence produces the longest flight time for a given quantity of fuel when flying at its[...]
Describe the departure profile segments (sectors) 1 to 4.
The various segments and other terms relating to the takeoff flight path are as follows: Reference zero. Defined as the ground point at the end of the takeoff distance, below the net takeoff flight path screen height. First (sector) segment. Extends from the reference point (35-ft height) to the point where the landing gear is retracted at a constant V2 speed. Second (sector) segment. Extends from the end of the first segment to a gross height of between at least 400 ft and a usual maximum of 1000 ft above ground level (AGL) at a constant V2 speed. Third (sector) segment. Assumes a level-flight acceleration during which the flaps are retracted in accordance with the recommended speed schedule. Fourth and final (sector) segment. Extends from the third segment level-off height to a net height of 1500 ft or more with flaps up and maximum continuous thrust.
Describe the weight, altitude, and temperature (WAT) limits.
The weight, altitude, and temperature (WAT) conditions limit the aircraft's MTOW (or MLW) so that it meets the required second segment (and missed approach) climb gradient performance with one engine inoperative given the ambient aerodrome conditions of pressure altitude and temperature (density).
What is VMU speed?
This is the minimum demonstrated unstick speed at which it is possible to get airborne on all engines and to climb out without hazard.
Describe tire speed limits.
Tire speed limit restricts the aircraft's maximum takeoff weight (MTOW) given the ambient aerodrome pressure altitude, temperature, and wind conditions so that the VR (liftoff speed) is less than the maximum rated ground speed limit for the tires to protect against the tires blowing out during the takeoff roll.
