Climb & descent

032 PerformanceChapter 3

Climb gradient and ROC

Formula — Climb gradient

CG % = (Thrust − Drag) ÷ Weight × 100
     = Height gain ÷ Distance × 100

ROC = TAS × (Thrust − Drag) ÷ Weight
    = TAS × CG
    = Climb gradient (%) × TAS × (6080 ÷ 60)   [ft/min, kt]

Climb angle (°) ≈ Climb gradient (%) × (3 ÷ 5)

Key fact

Load factor in climb = Lift ÷ Weight = cos(γ) where γ is flight-path angle. Load factor is less than 1 because thrust offsets the difference. sin(γ) = (Thrust − Drag) ÷ Weight.

Key fact

Maximum rate of climb = VY — dependent on excess power (PA − PR) ÷ W. Maximum climb gradient = VX — jets at VMD, props ≈ VMP. Highest gradient when aircraft is clean.

Ceilings

Ceiling	Definition
Absolute	0 fpm ROC
Service	100 fpm ROC (prop); 500 fpm ROC (jet)
Performance	300 fpm ROC AEO
Optimum altitude	Highest specific range — increases as weight decreases (jets)

Exam trap

Service ceiling: prop 100 fpm, jet 500 fpm. Do not confuse with performance ceiling at 300 fpm AEO.

CLTOM limiting factors

Key fact

CLTOM reduced when: temperature ↑, pressure altitude ↑, engine bleeds on. Any flap deflection reduces CLTOM (reduces ROC). Prevailing winds do not affect CLTOM. Flap extension reduces stall speed (reduces TORR) but any deflection increases drag and reduces climb.

Descent

Formula — Rate of descent

ROD = TAS × (Drag − Thrust) ÷ Weight
    = TAS × sin(γ)

DG % = Height loss ÷ Range × 100
     = (Drag − Thrust) ÷ Weight × 100

Glide performance

Key fact

Glide angle affected only by AoA and configuration — minimum at VMP. Heavier aircraft: higher IAS and ROD but same glide distance. Lighter aircraft glides longest time (endurance). VMP — max glide endurance (min ROD). VMD — min drag, max glide range.

Exam trap

Glide range increases when CL is reduced. In a descent at constant Mach, IAS increases (pitching down) → CL decreases → descent angle increases.

OEI climb — critical engine

Key fact

Critical engine — worst engine to fail (highest yaw moment). For clockwise props, critical engine is the left. Into-wind engine fails for counteracting props. OEI failure increases VX, decreases VY, increases power required and total drag.

Class B climb requirements

Key fact

En-route minimum: 300 fpm all engines at max continuous power. Net gradient = gross + 0.5%. AEO climb gradient factored by 0.77 for VMC planning. Above cloud base, use OEI CG.

Class B approach and landing climb

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

Turning after take-off

Key fact

No turns below 50 ft (screen height). 0° bank below 50 ft. 15° from 50–400 ft. 25° above 400 ft. Accountability area width depends on visibility and track change (CAP MEP 3.1.1).

CG and weight effects

Key fact

Forward CG: increased fuel consumption, decreased range/endurance, increased longitudinal stability, increased stall speed, decreased absolute ceiling, decreased ROC — same as heavier aircraft. Aft CG: opposite — light pitch forces (overstress risk), increased range/endurance, decreased stall speed.