Cruise

Cruise is the longest phase of a normal flight. Efficiency, safety, and correct system management are decisive here.

Choosing cruise altitude

Factors:

Wind (WINTEM, GAFOR): use tailwind, avoid headwind.
Cloud base and tops (SIGWX, METAR): maintain VMC.
Airspace (charts): stay under / above active CTR/TMA.
Oxygen requirement under EU NCO.OP.205: above FL100 (10 000 ft) for crew/pax after 30 min; above FL130 (13 000 ft) immediately for all on board.
Sun position: avoid blinding sun on long westbound legs.
Fuel consumption: higher (best L/D ≈ 65 % power) for maximum range, lower for speed.

SERA.5005 (b) — VFR cruising levels

Magnetic track 0°–179° (eastern half): odd thousand ft + 500 (5500, 7500, 9500, 11 500 …).
Magnetic track 180°–359° (western half): even thousand ft + 500 (4500, 6500, 8500, 10 500 …).
Applies above 3000 ft AMSL or 1000 ft AGL (whichever higher).

Power setting

Consult POH: power/RPM/manifold combinations for cruise.
75 % power: fastest cruise, highest consumption.
65 % power: balance speed/consumption — recommended for normal flights.
55 % power: max range, slower.

Mixture

Above 3000 ft pressure altitude: lean for efficiency (POH).
Best power (richer): max RPM/CHT (climb, high power).
Best economy (lean of peak EGT): max range, lowest consumption.
Choice per POH and engine.

Engine monitoring during cruise

Every 30 min check:

RPM / manifold pressure: stable in the green.
Oil temperature: stable, in the green.
Oil pressure: stable, in the green.
CHT / EGT: stable (if monitored).
Voltmeter / ammeter: battery charging.
Fuel gauge: compare with plan.

Cruise anomalies — recognise and react

IAS drops, RPM constant, no visible icing

If the airspeed indication (IAS) continues to decrease in cruise, RPM stays constant, and no icing is detected, the likely cause is an iced pitot probe:

Switch pitot heat ON.
Watch: IAS should normalise within seconds to minutes.
If still abnormal: compare with GPS ground speed; use GPS as IAS substitute and land at the nearest field.

RPM reduces with controls unchanged

If in cruise the RPM decreases, with neither power lever nor mixture altered, the likely cause is incipient carburettor icing (see run-up lesson for temperature range):

Carb heat ON — as the ice melts, RPM initially rises (water through the carburettor) then stabilises.
After 1–2 min carb heat can be switched OFF and observe whether RPM remains stable.
If carb heat is permanently needed: change altitude or route.

Manifold pressure drops in level flight

For a constant-speed propeller (manifold pressure indication): if the manifold pressure in level flight gradually drops with the power setting unchanged, this is also an indicator of incipient carburettor icing (ice narrows the carburettor cross-section):

Carb heat ON.

Ammeter constantly in the negative range

If the ammeter shows constantly negative during the flight (battery discharging instead of charging) and the voltage regulator is verifiably not the cause (no voltmeter anomaly), the alternator/generator is faulty:

Switch off all non-essential power consumers (strobes, landing lights, GPS backup, avionics where possible) — the battery lasts about 30–60 min.
End the flight as soon as possible — land at the nearest suitable airfield.
Mayday/PAN-PAN not mandatory depending on remaining time reserve, but inform FIS.

Blocked static pressure port

A blocked static system (port clogged by insect, ice, or dirt) causes false altimeter indications (and false VSI and IAS too):

Symptoms: altimeter "stuck" or unrealistic; IAS and VSI wrong.
Open the alternate static source if available — usually a cockpit lever.
Without alternate static: the pitot-static system is impaired — proceed carefully by visual flight, GPS as altitude proxy.
Source: ICAO Annex 8, FAA-H-8083-25B Ch. 8 (Flight Instruments).

Logbook on technical defects

Technical occurrences in flight (e.g. generator failure airborne) must be entered in the logbook (aircraft technical log) — this is a duty under NCO.GEN.140 and ARC requirements. It informs the next pilot or mechanic, and the aircraft cannot be flown again without rectification.

When fuel won't reach destination before dark

If the pilot notices during a cross-country flight that he will not reach the destination before nightfall (and has no night-VFR rating), he must:

Land at the nearest suitable airfield while there is still adequate daylight.
If no airfield is reachable: perform a safety landing before it gets too dark.
Do not attempt to land in twilight — sight is lost, depth perception goes, stall risk is high.

FIS for weather information

In cruise, the Flight Information Service (FIS) can be contacted for information about active thunderstorms or other weather hazards along the route. The FIS desk has access to current SIGMET, AIRMET, and radar data and can inform the pilot about hazard development and re-routing suggestions.

→ Radio call e.g. "Munich Information, DEMRA, requesting thunderstorm activity on route Munich–Frankfurt."

Slow flight — CG dependent

Slow flight (low-speed near stall) is more critical with a tail-heavy CG (CG near or behind the aft limit):

Less longitudinal stability — harder to trim.
Reduced elevator authority in stall recovery.
Higher spin risk at stall.
→ Pilots prefer to train slow flight with standard CG, not in extreme tail-heavy configuration.

CG forward of the forward limit

A CG forward of the forward limit can cause take-off and flare complications:

Take-off roll is lengthened, because the nose is harder to raise (more elevator effort).
Flare on landing becomes complicated: elevator has insufficient authority to raise the nose to touchdown attitude — pilot cannot pull the nose into the flare → hard landing or nose-wheel-first.
Even with total mass under MTOM, a CG out of range is not permitted.

→ The pilot computes mass and balance before every flight (see Subject 030).

Risk: mass overrun

Exceeding the maximum take-off mass (MTOM) is forbidden and dangerous, because:

CG position can shift through additional loading (e.g. extra baggage far back).
Aerodynamic overload can cause structural damage or stall issues.
POH performance values no longer apply (all performance charts are based on MTOM or below).

Bird strike — risk also for GA

Bird strike is also a real risk for general aviation aircraft — not only for transport aircraft:

In a GA aircraft the bird can penetrate the windshield (especially at higher cruise speeds and larger birds such as geese, raptors).
Result: pilot injured or unconscious — aircraft uncontrollable.
Secondary danger: bird in the engine intake can cause power loss or fire.

Prevention: avoid bird-active times (dawn/dusk, migration); avoid low flight in bird-active zones; remain visually alert.

Lost orientation on cross-country

If the pilot loses orientation during a cross-country flight (no longer knows where he is), the standard procedure is:

Continue on planned heading to the next clear line of position (river, motorway, railway, coast, mountain ridge).
At that line determine the position (fly along until an identifiable point is found).
Re-orient and recompute heading to destination or diversion field.
If still uncertain: call FIS, declare PAN-PAN if needed, switch GPS on (if it was off for training reasons).

Every 10–15 min (see Subject 060):

Position fix (visual or GPS).
GS from time between waypoints.
ETA destination recomputed.
Wind checked → heading adjusted if needed.

Radio routine

FIS frequency for general information.
TMA/CTR calls before entry.
PIREPs to FIS for other traffic (turbulence, weather).

Airspace vigilance

Chart and position compared continuously.
Call before TMA/CTR entry in good time (often 10 min lead recommended).
Restricted/danger areas circumnavigated or NOTAM status checked.

Sterile cockpit

Recommendation: below 1000 ft AGL and during critical phases (TMA entry, frequency change) no private conversation, only flight-relevant communication.

Comfort aspects

Hot/cabin temperature: ventilate as needed.
Stomach-friendly: light meal before flight, water on board.
Toilet: no pressure noticed below 8000 ft; on cold/long flights a plastic bag as emergency.