Flight Performance and Planning (Mass and Balance, Performance, Flight Planning)
What the paper covers
Flight performance and planning combines mass and balance, take-off, landing and climb performance, and the flight plan itself. Expect chart work - entering a graph with two variables and reading a third - plus weight-shift arithmetic and fuel-leg calculations.
Mass and balance
- MTOW, maximum landing weight and maximum zero-fuel weight are hard limits; empty weight and empty CG come from the latest weighing report.
- Moment = weight × arm from the datum; total moment divided by total weight gives the CG, which must lie inside the envelope for take-off and landing.
- %MAC = (CG − CG at the leading edge of the MAC) ÷ MAC length × 100.
- Moving weight: shift = weight moved × distance moved ÷ total weight.
Performance
- Convert aerodrome elevation to pressure altitude, then temperature to density altitude; high, hot and humid means a longer ground roll, weaker climb and a lower service ceiling.
- Take-off distance grows with weight, tailwind, upslope, soft or wet surfaces and higher density altitude; landing distance is affected by the same factors plus braking action.
- V speeds come from the AFM: Vr, Vx, Vy, and the approach speed, usually 1.3 Vso.
Flight planning and fuel
- Fuel = taxi + trip + contingency (typically 5% of trip) + diversion or alternate + final reserve (30 minutes VFR by day, 45 minutes IFR).
- Build a plog: leg distance, forecast wind, TAS, then heading and ground speed from the wind triangle, then time and fuel per leg.
Worked example
Aircraft all-up weight 3400 lb with CG at 82.0 in aft of datum. You move 100 lb from station 40 in to station 120 in. CG shift = (100 × 80) ÷ 3400 = 2.35 in aft, giving a new CG of 84.35 in. Check that 84.35 in is inside the aft limit and that weight is still under MTOW - moving weight does not change total weight, but adding or removing it does.
Traps that cost marks
- Mixing units: US gallons against imperial gallons, litres against kilograms of fuel at about 0.72 kg/L, pounds against kilograms.
- Reading performance charts with pressure altitude when density altitude is required.
- Using TAS instead of ground speed for time and fuel.
- Forgetting to recompute the total moment when weight is added at a station.