Descent

The descent transitions the aircraft from cruise altitude to pattern or approach altitude. With performance planning and engine management it is relaxed; without it, it becomes a hectic "rush" at the field.

Standard descent profile

rule (see Subject 060): 3 NM distance per 1000 ft altitude loss.

Descent from 5000 ft to 1500 ft = 3500 ft = 3.5 × 3 = 10.5 NM.
At 100 kt GS, 10.5 NM takes 6.3 min.
Descent rate ≈ 500 fpm (typical 3° descent at 100 kt GS).

Beginning the descent

Rule of thumb (POH-specific):

Altitude to lose: cruise − pattern altitude (+ 100 ft buffer if needed).
Distance to descend: above value / 3 (NM).
Plus 1-2 NM for pattern stabilisation.

Engine management

Reduce power in stages (e.g. 200 RPM at a time), not abruptly → avoid shock cooling of the engine.
Mixture richer when descending into denser air.
Carb heat ON before descent (carbureted engines) — low power increases carb icing risk.
Engine gauges monitored: CHT/oil temperature should not drop suddenly (crack risk).

Speed management

At low power: aircraft descends slowly, GS barely rises.
At normal cruise power + nose down: rapid descent, GS rises — do not exceed Vno.
In strong descent: respect Va in turbulence.

Frequencies and airspace

TMA/CTR approach frequency called in good time (10 min lead).
ATIS of destination listened (wind, runway, QNH).
Squawk as assigned.
Altimeter to QNH below transition level.

Altimeter setting

Transition level → below: altimeter from standard (1013) back to QNH.
Result: indicated altitude in ft AMSL instead of FL.
Cold-temperature correction (see Subject 050), especially in winter and mountain terrain.

Descent sequence

5–10 min before TOD: ATIS, frequencies, approach briefing.
At TOD: power reduced to ~65 % or POH cruise descent, sink rate ~500 fpm.
Carb heat ON, mixture watched.
Passing transition level: altimeter QNH.
CTR/TMA call with position and altitude.
Reach pattern altitude: 1000 ft AAL (typical); level off, power for pattern speed.
Pre-landing check (FUEL-Mixture-Trim-Lights-Hatches-Harnesses; specific to school).

When cloud base drops further during descent

If the pilot notices that the cloud base continues to descend in the direction of flight and meteorological VMC conditions are still just maintained (e.g. SERA minima still met), the pilot should:

Turn back and land at the nearest suitable airfield.
Do not continue toward the descending cloud base — the risk of entering IMC is high.
Even if currently still VMC: forecast deterioration is reason to divert.

Approaching a mountain pass

General rule for approaching a mountain pass:

Aim for the centre of the pass — not on one side, but centrally.
Altitude reserve above pass altitude (rule of thumb +1000 ft).
With adequate speed (above normal cruise) to compensate downdrafts.

Flying in mountainous terrain — main danger downdrafts

Flights in mountain ranges can be especially dangerous because downdrafts (lee descents, mountain waves) may not be overcomeable by engine power:

A downdraft can be 1000-2000 fpm — far exceeding the climb rate (~700 fpm) of a light aircraft.
→ Pilot is forced into an uncontrollable descent, even with full power.
Consequence: avoid mountain waves from the start, stay clear of lee sides.

Lee effects even at moderate wind

Even at moderate wind speeds (10-20 kt at the mountain), significant lee effects and strong up- and downdrafts must be expected. A seemingly "harmless" wind can on the lee side of a mountain:

Produce downdrafts > 1000 fpm.
Create turbulence with g-fluctuations.
Generate mountain waves even at considerable distance.

→ In mountain flight: prefer the windward side, sufficient altitude (> 2000 ft above the highest point in sight).

Hail shower in cruise

If a severe hail shower is unexpectedly encountered, the pilot should:

Reduce speed to Va (maneuvering speed) or below — minimise structural load from hail + turbulence.
Carb heat ON — hail and precipitation can cause carb icing immediately.
Leave the shower as quickly as possible — identify the shortest route out (often sideways or behind, not through).
In larger hail (> 2 cm): structural damage to windshield, wing leading edges, cowling — be ready for an emergency landing.

Lightning strike

If the aircraft is struck by lightning (typical near CB), the following effects can occur:

Crew dazzle by the bright flash — temporary loss of sight for seconds to minutes.
Electronic-device interference — avionics may fail, GPS, COM, NAV; reset may be needed.
Mechanical damage — small holes at entry/exit points, damaged antennas, possibly structural damage.
Magnetic compass failure — the compass can be permanently mismagnetised by the lightning magnetic field; a compass swing (re-calibration) is needed after flight.

→ On lightning strike: inform ATC, declare mayday/PAN-PAN, check avionics status, fly to the nearest suitable field, report to maintenance.

Cabin door opens after lift-off

If the cabin door suddenly opens after lift-off (pilot forgot to close it, latch faulty), the pilot should:

Stay calm — the door typically cannot open further against the airflow, the aircraft flies on.
Fly a standard pattern and return for landing — do not try to close the door in flight (distraction, control loss).
Do NOT continue to cruise, do not continue the flight.
On the ground: close the door properly, check the latch.

Descent risks

Cabin/sinus pressure equalisation: too rapid a descent can cause eardrum pain (Subject 040). Sink rate < 500 fpm with passengers with a cold.
Carb icing: at low power and humid air — carb heat ON.
Disorientation: VFR descent in cloud not permitted.
Fuel cavitation: in strongly uncoordinated descent (slip) the fuel inlet may partially dry.