This is explanations of some of the terms used in relation to aircraft performance.
Such as speeds, weight and balance calculation and loadsheet.|
- IAS = Indicated Airspeed = airspeed indicator reading.
- CAS = Calibrated Airspeed = IAS corrected for static position error.
- EAS = Equivalent Airspeed = CAS corrected for compressibility error.
- TAS = True Airspeed = EAS corrected for OAT and pressure altitude.
- GS = Ground Speed = TAS corrected for wind component.
- M = Mach number = relationship between TAS and speed of sound.
- EPR = Engine Pressure Ratio.
- FF = Fuel Flow.
- MCT = Max Continuous Thrust.
- RPM= Revolutions Per Minute.
- OAT = Outside Air Temperature.
- RAT = Ram Air Temperature = TAT.
- SAT = Static Air Temperature = OAT.
- TAT = Total Air Temperature = RAT.
- BA = Braking Action.
- CG = Center of Gravity.
- µ = friction coefficient.
- FL = Flight Level.
- GWC = Gross Weight Chart.
- RC = Rate of Climb.
- RTO = Rejected Takeoff.
- RWY = runway.
- SL = Sea Level.
- T/O = TKOF = takeoff.
- TODC = Takeoff Data Computer.
Min. Control Speed on Ground VMCG is defined as the minimum speed at
which directional control on ground can be recovered after lateral deviation of
max 30 ft and maintained under the following conditions:
Note - VMCG determines the lowest V1 to be used.
- Sudden engine failure on the most critical engine.
- Takeoff thrust on the remaining engine(s).
- Most critical takeoff configuration, normally smallest takeoff flap, unless
a VMCG is established for each takeoff flap configuration.
- Most unfavorable TOW an CG position.
- Control maintained by rudder only.
Min. Control Speed Airborne VMCA is defined as the speed at
which directional control can be recovered and maintained in flight under the
Note - This speed is used in determining VR and V2.
- Sudden engine failure on the most critical engine.
- Takeoff thrust on the remaining engine(s).
- Flaps in the smallest position.
- Landing gear up.
- Zero yaw or an angle of bank not in excess of 5º.
The 5º bank is used by the manufacturer in certification of VMCA.
The effect in speed of this bank differ from one aircraft type to another.
For wings level flight the VMCA will be in the order of 15 kt
for MD-80/90/DC-9. VMCA problem do normally only occur at low takeoff
weights. At high weights VMCA is overruled by the stalling speeds, and
directional control can be maintained with wing level, practically without any
sideslipping. Consequently, the wings level technique is used because more emphasis
is placed upon aircraft climb performance at high weights. At low eights the
performance capability normally is in excess of that required, so favorable bank
angle may be used for heading control if necessary.
V1 = Decision speed is the speed at which, for the purpose of
determining the required takeoff runway length, engine failure is assumed to be
recognized and the rejected takeoff initiated. The reaction time used in the
calculation is about 1 second. Thus for calculation of the required runway
length, the engine failure is assumed to occur 1 s before V1. The
total time for pilot actions , until full brakes are applied, is the time
demonstrated during certification plus two seconds (typically 3-4 seconds).
At V1 it should be possible to either:
Note - In certification, stopping from V1 is based on the most
efficient wheel braking on a dry runway without credit for reversing. The
performance in an actual accelerate-stop case may differ from the demonstrated
performance due to a number of reasons such as worn or lost brakes, excessive pilot
reaction time, etc. The benefit of reversers is very small on top of max braking
on a dry runway. Thus, stopping from V1 at a runway limited weight is
a very critical task.
Reduced V1 (15 ft screen height) is possible to use. In
connection with reduced braking action, as on a wet runway, a rejected takeoff
close to V1 becomes even more critical than described above. For
such cases, a reduced V1 can be used to transfer safety margin from
the continued takeoff case to the rejected case to better balance the margins
between the two options.
- Reject the takeoff and stop at the end of the runway.
- Continue the takeoff and reach 35 ft at V2 speed at the end
of the runway.
In accordance with CAA regulations, V1 on wet and contaminated runway
is based on obtaining 15 ft at the end of takeoff distance instead of the normal
35 ft. Takeoff weight calculations must be designed to consider V1
reductions. Otherwise the contamination may degrade acceleration, after the
engine failure, so the aircraft will not lift off before the end of the runway.
VR = Rotation speed is the speed at which, for the purpose
of determining required takeoff runway length, rotation of the aircraft is
VR must be determined not to be less than:
V2 = Takeoff safety speed is the speed used to determining
the performance during the initial climbout. In these calculations, V2
should be reached prior to attaining a height of 35 ft above the runway surface.
- 1.05 times the minimum control speed, airborne.
- A speed which permits the attainment of V2 prior to reaching
35 ft height at the end of the takeoff distance.
- An upper limit for VR is set to max tire speed.
Thus V2 is used in determining:
V2 shall not be less than:
- The required takeoff distance, prior to the end of which it should be
- The climb requirements limitaions.
- The obstacle clearance limitaions.
In practise, V2 should be used as climbout speed in case of engine
failure until the aircraft has attained a safe height above obstacles in the
takeoff direction. Flying at speeds below V2 will result in considerable
loss in climb performance and may crate problems regarding stall.
VFl up and VSl in are minimum speeds for retraction of FLAPS
and SLATS after takeoff.
VClean is the speed to be used in the final segment of a takeoff
with engine failure, i.e with "CLEAN" aircraft (after flap/slat retraction).
VP = Pattern speed is "maneuvering speeds" and gives better margin
to stall. Used in low level holdings, procedure and circuits.
VP clean "PATTERN CLEAN", normally the lowest speed with all
VMO Max operating IAS, limited by structural requirements.
MMO Max operating Mach, limited by high speed aerodynamics.
Rough Air Speed is the speed which should be used in connection with
VHOLD Speed to be used during holdings. Below FL 250 the same
as VP clean. FL 250-290 VP clean + 10 kt. Above FL 290
VP clean + 20 kt.
Vref is reference speed used to derive other speeds for different
phases of flight by adding of fixed increments. The amount to be added are stated
in the respective aircraft operating manual. When Vref is used without
additional flap suffix, it is based on the full landing configuration. Occasionally
it is necessary to use Vref based on other flap setting. In such cases
the configuration is always indicated as a suffix (Vref 20).
Landing runway length requirements are based on Vref at 50 ft over
the runway threshold.
VTH For aircraft not using Vref, landing runway
length requirements are based on VTH at 50 ft over the runway
- 1.1 times VMCA.
- 1.2 times VS.
Weight and balance.
In connection with issuance of loadsheet and flighplan, some specific load
control terms are used. This table shows the explanation in alphabetic order.
BW = Basic Weight. Basic empty weight, including:
DOW = Dry Operating Weight. Operational empty weight. Basic weight
plus operational items such as crew and pantry (equipment, food, beverages).
LW = Landing Weight. Takeoff weight minus trip fuel.
MLW = Maximum Landing Weight. Weight limitation for landing, governed by
structural and/or operational requirements.
MTOW = Maximum TakeOff Weight. Weight limitation for takeoff (brake release),
governed by structural and/or operational requirements.
MZFW = Maximum Zero Fuel Weight. Structural weight limitation.
RW = Ramp Weight. Takeoff weight plus taxi fuel, i. e. weight of loaded
aircraft before starting the engines.
TOW = Takeoff Weight. Gross weight of aircraft at brake release for takeoff,
i.e. actual zero fuel weight plus takeoff fuel.
ZFW = Zero Fuel Weight. Dry operating weight plus total traffic load.
Ballast fuel. Non-usable fuel used for balancing purpose (only possible
on some aircraft). The ballast fuel is separated from takeoff fuel (usable fuel)
and loaded ia a separate tank. the fuel must not be consumed or jettisoned
Block fuel. Weight of total amount of fuel on board before starting taxi.
Burn-off fuel. Taxi fuel plus trip fuel.
Reserve fuel. Difference between takeoff fuel and trip fuel, consiting of:
- aircraft structure.
- unremovable equipment.
- unusable liquids (fuel, oil and others).
- standard loose equipment.
Taxi fuel. Weight of fuel to cover APU consumption, engine start and ground
maneuvers until start of takeoff. Standard weights are used which are, with a few
exceptions, applicable at every airport.
TOF = TakeOff Fuel. Weight of total usable fuel onboard at the moment of
takeoff (brake release).
Trip fuel. Weight of the precalculated fuel consumption from takeoff to
touchdown at the next point of landing.
Allowed traffic load. The weight remaining after the subtraction of the
operating weight from the allowed takeoff weight.
Deadload. Total weight of:
Total traffic load (total payload). Total weight of:
- Route reserve,
- holding, and
- additional fuel.
Underload. difference between allowed traffic load and load actually
BI = Basic Index. Center of gravity at basic weight (BW) expressed
as an index value.
CG = Center of Gravity. Point about which an aircraft would be balanced
DOI = Dry Operating Index. Center of gravity at dry operating weight
expressed as an index value. Basic index (BI) corrected for the
balance influence of the loads included in dry operating weight (DOW).
DLI = Dead Load Index. Dry operating index (DOI) corrected for
the balance influence of the load in compartments.
LIZFW = Loaded Index at Zero fuel weight. Deadload index (DLI) corrected
for the influence of passengers in cabin (fuel not included).
MAC = Mean Aerodynamic Chord. Imaginary reference line (chord) dividing
the wing areas producing the same amount of lift. Location of CG of loaded
aircraft is given as a percentage of the MAC.