Class A Approach and Landing - ATPL 032 — Performance

A class A landing is decided twice: once in the sky, where two certified climb gradients guarantee the aeroplane can always throw the landing away, and once on paper at dispatch, where the demonstrated stopping distance must fit inside a heavily discounted runway. This lesson works through both, then through everything that stretches the real stop, and ends at the brakes, still hot, asking how soon the aeroplane may fly again.

Two go-arounds, two guarantees

Certification refuses to let the landing become a trap: whatever happens on final, the aeroplane must be able to climb away. CS-25 writes that promise twice, for the two ways a go-around can be flown:

Approach climb (CS-25.121(d)) — the engine-out go-around: critical engine inoperative, the rest at go-around thrust, gear up, approach flaps, demonstrated at the maximum landing weight, at a speed from normal procedures but not above 1.4 VSR; the gradient may not be less than 2.1% / 2.4% / 2.7% for two-, three- and four-engined aeroplanes.
Landing climb (CS-25.119) — the all-engine baulked landing: gear down, landing flaps, at VREF, using the thrust actually available 8 seconds after the throttles leave minimum flight idle; the gradient may not be less than 3.2%.

Both are thrust-versus-weight promises, so both surrender to the atmosphere: high aerodromes and hot days cut the thrust, and the climb-limited landing mass falls with it, the landing's own WAT limit. On a hot day at a high airport it is often this pair, not the runway, that names the maximum landing mass.

The demonstrated distance and the dispatch discount

The certified demonstrated landing distance (CS-25.125) runs from 50 ft above the threshold to a full stop on a dry, level runway, crossing the screen at VREF, flown by a test crew with no reverse thrust credited. It is a superb number produced under conditions no line flight repeats, and the operational rules discount it accordingly. The landing distance available (LDA) is the runway length declared available and suitable for the ground run of a landing aeroplane, and at dispatch the demonstrated distance must fit inside a fraction of it:

Dry (CAT.POL.A.230) — a full stop within 60% of the LDA for turbojets, within 70% for turboprops.
Wet (CAT.POL.A.235) — the required landing distance becomes 115% of the dry requirement, unless the AFM carries specific approved wet data.
Contaminated — the greater of the wet requirement and 115% of the contaminated landing distance from approved data.

Dispatch also has to guess the runway. The rule makes it guess twice: the mass must work for a landing on the most favourable runway in still air, and separately on the runway most likely to be assigned given the forecast wind, with the usual wind accountability of 50% of headwind and 150% of tailwind applied. Three speeds anchor the approach that all of this assumes:

VSR0 — the reference stall speed in the landing configuration.
VREF — the landing reference speed at the 50 ft screen: not less than 1.23 VSR0, not less than VMCL, and fast enough for the required manoeuvre capability.
VMCL — the minimum control speed for approach and landing: the slowest speed at which control can be kept with the critical engine failing while the rest go to go-around thrust in the landing configuration.

What stretches the stop

The landing obeys the same physics the take-off did, with the signs reversed. A downhill slope and a tailwind both stretch the ground roll and cut the field-limited landing mass, tailwind again counted at 150 per cent; high and hot means more TAS behind the same VREF, more energy to kill, and a longer distance from the same 50 ft. The runway surface writes the friction available, and the deceleration devices decide how much of it is collected:

Ground spoilers — dump the wing's lift onto the wheels; without that weight the brakes have almost nothing to work with, which makes spoilers the quiet hero of every short stop.
Anti-skid — holds each wheel at peak braking; with it inoperative the distances grow severely and the dispatch penalty is one of the largest in the book.
Reverse thrust — no credit in the dry certified distance, but credited in wet and contaminated data, where it does its best work: reverse does not care how slippery the runway is.
Autobrake — schedules a deceleration rate rather than a distance; a high setting approaches the anti-skid limit, a low one trades runway for brake wear and comfort.

On a wet or contaminated runway the hydroplaning lesson returns to land: the wheels arrive unspun, planing at the lower 7.7 √P threshold, so the technique is a firm touchdown to break the water film, spoilers immediately to plant the wheels, and reverse early, because reverse is the one decelerator that works while the tyres still cannot grip.

The quick turnaround limit

A landing pours the aeroplane's kinetic energy into the brake packs, and the heat does not leave with the passengers. The next take-off must still be able to absorb a maximum-energy rejected take-off, and brakes that start hot cannot. The AFM's quick turnaround limit gives a landing mass above which the aeroplane must wait a specified cooling time (or have the brakes inspected) before departing again; hotter still, and the wheels' fusible plugs may melt and deflate the tyres by design, rather than let them burst. Heavy landing, high aerodrome, tailwind, minimal reverse: the very landings that heat the brakes most are the ones that press this limit.

State the CS-25 approach-climb and landing-climb requirements and the effect of temperature and pressure altitude on them

Describe the demonstrated landing distance, define the LDA, and apply the dry/wet/contaminated field-length rules and dispatch runway assumptions; define VSR0, VREF and VMCL

Explain the effects of slope, surface, wind, temperature and pressure altitude on landing mass, the deceleration devices, and hydroplaning management

Describe how brake temperature limits turnaround times

Two go-arounds, two guarantees

The demonstrated distance and the dispatch discount

Check you understood

What stretches the stop

The quick turnaround limit