Performance Flashcards
Clearway requirements
- shape
- width
- max slope
- obstacles
Rectangular
>500ft wide
Upward slope <= 1.25%
No protruding object or terrain, except lights if 26in or less above the runway and to each side of it.
Balanced field
TODA = ASDA
(i.e. stopway = clearway)
Balanced field take off
- description
- effect of added clearway/stopway
TODR = ASDR [note: required]
Maximises mass by using choosing a V1 that balances ASD and TOD requirements.
Extra clearway allows lower V1 (longer at OEI speed) to increase mass.
Extra stopway allows higher V1 (longer stopping distance) to increase mass.
Amendments to TODA
Max TODA = 1.5 x TORA
So clearway over 50% of runway length can’t be fully used.
Flight path angle designations
We assume wing chord in line with longitudinal axis.
Correction for density altitude from pressure altitude
120ft per degree C (difference to ISA)
Jet power
Jet power = thrust x TAS
Generally thrust is constant so get a straight line relationship with TAS.
Speeds in 1/2 rho V^2
V is TAS
However the total dynamic pressure element of 1/2 rho V^2 relates to CAS/EAS.
Which speed is used to asses power required, V(MP) etc?
TAS
This is because power is defined as thrust x TAS.
V(R)
V(LOF)
V(2)
V(R) = Speed at which you rotate
V(LOF) = Lift off speed, slightly higher than V(R)
V(2) = Speed at the screen height (end of TOD) which will be higher still [aka Take off safety speed]
Using headwind and tailwind in take off distance calculations
Use 150% of tailwind and 50% of headwind for margin of safety.
V(stop) and V(go)
V(stop) is the speed above which the aircraft can’t be stopped within the ASDA.
V(go) is the speed below which (based on engine failure) rotation at V(R) and reaching V(2) at 35ft screen height is not possible.
Both vary with mass and are probabilistic lines (i.e. 50:50 chance of making it).
V(stop) and V(go) plotted against mass
One Engine Inoperative
Field Length Limited
Take Off Mass
(OEI FLL TOM)
OEI FLL TOM is where V(go) = V(stop) = V(1) - called the decision speed
i.e. highest mass at which there is no “die” portion of the V(stop) & V(go) chart!
V(EF)
Speed at which an engine failure is assumed to occur. CS25 allows a minimum 1 second delay between V(EF) and V(1) to account for startle effect.
Referred to as “recognise and REACT” in exam, although react doesn’t include starting braking.
Changes for wet runway takeoff
V(EF) is reduced by 10kt, with correspondingly lower V(1) speed.
We are further from V(R) at this point so TOD will increase. Therefore screen height is reduced to 15ft (for OEI only!), with V(2) only required at the eventual 35ft point.
TO performance calculations for wet runways - process
Need to calculate for wet and dry and use worst case scenario.
TODA: Wet runway with 15ft screen (and slower V(1)) may or may not be more limiting than dry with 35ft.
ASDA: Calculate for wet and dry (with respective V(1wet) and V(1dry)) and also for all engines & engine out. Use the most limiting length.
Reverse thrust and ASD required (ASDR)
Reverse thrust can only be factored in for wet runway stopping, not dry runways
Other restrictions on V(1)
V(MBE) - V(1) must be less than V(MBE) otherwise brakes can’t cope with the rejection.
V(1) must be above V(MCG) to ensure control can be maintained for any continuation above V(1).
All Engine Operating
Field Length Limited
Take Off Mass
(AEO FLL TOM)
This is the TOM restriction based on all engine calculations (with 1.15 safety factor, as it is a likely event).
In typical case this is a vertical line on the V(stop)/V(go) chart which will be higher than the OEI FLL TOM intersection with V1.
If lower (e.g. 4 engine) it will be to the left of the V1 intersection. V1 still valid but that TOM can’t be achieved.
TORA vs TODA limitations
Need to get to half of the screen height by end of TORA.
With no clearway TODA will be the limitation, but as clearway increases TORR becomes a limiting factor.
TORR
The longest of:
OEI dry: TOR + half distance to 35ft
[OEI wet: TOR + distance to 15ft, if wet!]
AEO: 1.15 x (TOR + half distance to 35ft)
V(2) minimums
Max of
- 1.1 x V(MC)
- 1.13 x V(SR)
Take off climb limit
- relevant config
- required gradients
There is a minimum requirement for AIR climb gradient, based on gear up and OEI.
2 engines: 2.4%
Combined with altitude & temp data this produces a mass limitation, to be considered along with field length take off mass limits.
Cost Index
Operating Cost / Fuel Cost
Effect of cost index on climb
High cost index implies low fuel cost.
This would mean adopting fast speeds in general (subject to limits, e.g. 250kt <FL100). Climb gradients shallower. Top of climb reached later, but at a further ground distance so trip time reduces.
Buffet boundary limit
Restricted on slow side by stall speed and high side by mach limit.
As altitude increases these close in together, creating “coffin corner”.
Increased mass brings both in (mostly the stall speed), thus reducing maximum altitude.
Buffet boundary limit
- Load factor
Increased load above 1g (e.g. due to turbulence) brings in the two limits. Thus buffet boundary charts usually based on 1.3g to give some margin for safety.
Need awareness that increased turbulence could take you outside safe operating conditions.
Missed approach climb gradients:
OEI
AEO
OEI: 2.1%
AEO: 2.5%
AEO (landing climb): 3.2%
V(REF)
- description
- value (class A)
Landing reference speed.
This is your speed at screen height.
Will usually be V(REF) + 10kt on approach, V(REF) - 10kt at touchdown.
V(REF) = 1.23 x V(SRO) class A
Not less than V(MCL)
Impact of failure on LDR
- anti skid brakes
- reverse thrust
Anti-skid: +50%
Reverse Thrust: +10%
[Much higher for prop aircraft]
Runway landing distance factors if Wet
1.15
Landing distance safety margin
Jet: Land within 60% of LDA
Obstacle clearance
- Class A Net Take Off Flight Path (NTOFP)
For performance calculation purposes we consider engine failure at V(EF).
i) End of TODR (35ft) to gear up point, flown at V(2)
ii) From gear up to level flap retraction (c. 400ft), also V(2) with take off thrust
iii) [Level] segment for flap retraction, ends when in clean config. Accelerate to final segment climbing speed and reduce thrust on remaining engine to max continuous (MCT)
iv) Climb to at least 1500ft, at a climb speed (eg V(X)).
Obstacle clearance
- En-route obstacle clearance (Class A)
1000ft above terrain within 5nm of route while maintaining height
2000ft during driftdown stage
This is about dealing with engine loss in flight. You would generally use MCT for as long as possible to maintain altitude and diagnose, before driftdown to a level where height can be maintained.
Can assume fuel dumping to help with driftdown.
Flex take off
If TOW is less than MTOW, can use an assumed OAT (greater than actual) in FMS. FMS will use a lower fuel rate based on the higher assumed ambient temperature, reducing thrust and OEI limitations will just be achieved.
V(MCG) and V(MCA) for flex take-off
Because full thrust is available even on flex take-off, V(MCG) and V(MCA) must be calculated based on full thrust.
Otherwise there is a risk of failure to control aircraft if full thrust is applied.
Conditions when flex take off is not allowed
- Icy (or very slippery) runways
- Contaminated runways
- Anti-skid unserviceable
- Reverse thrust unserviceable
- Increased V(2) procedure
- Power Management Computer off (MRJT1)
Conditions when flex take off MAY not be allowed
Wet runways require suitable performance accountability (which in practice is the case for most operators). So wet runways ARE allowed.
Not recommended if windshear expected after takeoff.
Derated thrust take-off
- description
- possible on contaminated runways?
AFM must contain a complete set of performance calculations based on a limited thrust setting for the engines. This derated thrust setting can then be selected in FMS.
Unlike flex take-off this is considered to be a “normal” take-off, so no restrictions for contaminated runways (etc.)
V(MCG) and V(MCA) for derated thrust take-offs
For derated take-offs they will be reduced based on the lower available thrust.
This does however mean that TOGA thrust CANNOT be selected during derated thrust take-off. Likely to be restricted until flaps fully retracted.
Dynamic hydroplaning speed calc
9 x sqrt(psi)
7.7 for static wheel, but this is likely to be viscous not dynamic hydroplaning
Viscous hydroplaning
- description
- speed calc
When a thin film of liquid prevents the tyre contacting the runway, LIKELY AT RUNWAY THRESHOLDS.
Speed = 7.7 x sqrt(psi)
Reverted rubber hydroplaning
Can happen after a skid where high temperature in tyre boils and turn layer of water and vaporised rubber to steam.
Regulated vs structural vs performance mass limits
Structural are calculated from aircraft weight limits (MZFM etc.).
Performance are based on the runway calculations, V(1), V(2) etc.
Regulated mass limit is the lower of the two.
