Class B prop

032 PerformanceChapter 6

Class B definition and phases

Key fact

Class B: propeller aircraft, MOPSC ≤ 9, MTOW ≤ 5700 kg. Flight phases: take-off (BRP to 50 ft) · climb (50 ft to 1500 ft AGL) · landing (50 ft to full stop). En-route min climb: 300 fpm all engines.

Performance data chain

Key fact

CAP gives gross performance → aerodrome-specific factors → gross specific → regulatory factors → net performance. ASDA graph gives net performance, assumes no stopway or clearway. Graph questions give net data (no extra factors needed).

Take-off speeds — Class B

Definition — Multi-engine

VMC — minimum control speed with 5° AoB, ≤ 1.2 VS1. Take-off safety speed = 1.1 × VMC.

Definition — Single-engine

Take-off safety speed = 1.2 × VS1.

Key fact

VR must be higher than VS1. Speed at 50 ft: safe speed under reasonable conditions, ≥ 1.2 VS1. Minimum 4% climb gradient at take-off power, flaps take-off position.

Balanced vs unbalanced field

Key fact

No stopway/clearway: TORR = TODR (gross) × 1.25. With stopway/clearway: TORR = TODR (gross) × 1.0 · ASDR = TODR (gross) × 1.3 · TODR = TODR (gross) × 1.15. FLLTOM from shortest of these distances.

Formula — Slope and surface factors (CAP SEP 2.1.1)

Take-off:  1% upslope × 1.05  ·  Dry grass × 1.2  ·  Wet grass × 1.3
Landing:   1% downslope × 1.05  ·  Grass × 1.15  ·  Wet × 1.15
Regulatory LDR = LDR (gross) × 1.43

Wind factoring and obstacle clearance

Key fact

Minimum 50 ft clearance. Use factored winds: 50% headwind, 150% tailwind. Distance to obstacle = GS × height gain ÷ ROC × 100.

Exam trap

Upslope: TOD +5% per 1% upslope. Downslope landing: LDR factor +5% per 1% downslope. 1% = +0.05 in factor tables.

MEP additional requirements

Key fact

Same as SEP, plus: critical engine failure increases VX, decreases VY. Net gradient = gross + 0.5%. AEO climb gradient factored by 0.77 for planning in VMC.

Key fact

AEO climb gradient: 4% at screen height. OEI: measurably positive at 400 ft · 0.75% at 1500 ft (CAP MEP 3.1.2).

Approach and landing climb — MEP

Phase	Requirement
Approach climb (go-around during approach)	2.5% CG
Landing climb (balked landing, before touchdown)	0.75% CG

Key fact

VREF ≤ 1.3 VSO. Landing factors in CAP MEP 5.1.1. All requirements in CAP MEP 5.1.2/5.1.3.

VMC and critical engine

Key fact

VMC — enough speed to maintain control with 5° AoB, ≤ 1.2 VS1. For clockwise props, critical engine is left. Into-wind engine failure for counteracting props.

Planning calculations

Formula — Wind component

Wind effect = Wind speed × cos(angle difference)

NAM ÷ TAS = NGM ÷ GS

At reference zero subtract/add 50 ft. Calculate pressure altitude if QNH ≠ 1013.

Key fact

ROC in VMC = ROC all engines × 0.77. ROC in IMC — assume OEI ROC. Time to cloud base: (cloud base − screen height) ÷ ROC VMC. Time above cloud: [(obstacle + clearance) − cloud base] ÷ ROC OEI. Distance = GS × total time.

Load factor and stall speed

Formula — Turn load factor

n = 1 ÷ cos(bank angle)

VS new = VS old × √(W new ÷ W old)

Sample graph answers (revision)

Key fact

SEP: 465 m (+18) · 1850 ft (+27) · 2375 ft (+30) · 4150 ft (+38) · 19500 ft (+30) · 3200 lbs (ISA) · 3500 lbs (+40) · 1140 / 10.6%. MEP: 2000 ft (+24) · 3450 ft (+20) · 3450 lbs (+10) · 4500 lbs (+5). MRJT: 5500 ft (O7) · 3100 m (2000 ft).