Night Flying

Night flying changes what a pilot can see, not how the aeroplane flies. The natural horizon fades or disappears, the ground below is a pattern of lights or simply dark, and the eye itself works differently. A forced landing may have to be made onto ground the pilot cannot see. The rules respond with extra requirements for licences, recent experience, lights, instruments and fuel.

This article brings those rules together for EASA and FAA pilots and summarises the human factors. The physiology is covered in depth in the eye and vision and visual illusions, the logbook rules in flight time logging and recent experience, and the weather minima in VFR, IFR and meteorological conditions.

Night defined

The Standardised European Rules of the Air (SERA) define night as the hours between the end of evening civil twilight and the beginning of morning civil twilight. ICAO's definition also allows the authority to set another period between sunset and sunrise. Evening civil twilight ends when the centre of the Sun's disc is 6° below the horizon; nautical and astronomical twilight, at 12° and 18°, have no operational meaning. Twilight lasts longest where the Sun's path meets the horizon at a shallow angle, so at 60°N in June summer nights practically disappear, while near the equator night follows sunset quickly (see time, sunrise and twilight).

The FAA uses three definitions for three purposes:

Night VFR rules and the night rating

Night VFR is allowed only where the State permits it. SERA then adds conditions: a flight plan if the flight leaves the vicinity of an aerodrome; two-way radio contact where a channel is available; a cloud ceiling of at least 450 m (1,500 ft); none of the reduced visibilities allowed by day; continuous sight of the surface at and below the higher of 900 m (3,000 ft) AMSL and 300 m (1,000 ft) above terrain; and, where the State sets no minimum altitude, a level at least 300 m (1,000 ft) above the highest obstacle within 8 km of the aircraft, or 600 m (2,000 ft) over high or mountainous terrain. States add their own detail. France, for example, requires night VFR flights to use aerodromes promulgated for it and raises the aeroplane minimum away from published routes to 450 m (1,500 ft) above the highest obstacle within 8 km. Under SERA, special VFR is granted by day only unless the authority permits otherwise.

A European LAPL or PPL holder needs a night rating (FCL.810) to fly VFR at night. The course comprises theoretical knowledge instruction and at least 5 hours of flight time at night, 3 of them dual including at least 1 hour of cross-country navigation with one dual cross-country flight of at least 50 km, plus 5 solo take-offs and 5 solo full-stop landings.

The FAA private pilot certificate has no separate night rating. Under FAA rules the weather minima tighten at night instead: in Class G airspace at or below 1,200 ft above the surface the day minimum of 1 SM clear of cloud becomes 3 SM with 500 ft below, 1,000 ft above and 2,000 ft horizontally from cloud. One exception remains: an aeroplane may fly a traffic pattern within half a mile of the runway with 1 SM visibility, clear of cloud. Special VFR between sunset and sunrise needs an instrument rating and an aircraft equipped for IFR, because 1 SM and clear of cloud at night amount to instrument conditions for a visual pilot.

Fuel reserves grow at night as well. Under AMC1 NCO.OP.125(b) the VFR final reserve rises from 30 to 45 minutes at holding speed at 1,500 ft above the destination; 14 CFR 91.151 raises it from 30 to 45 minutes at normal cruising speed. The figure follows the flight actually flown, so a late departure that lands after dark brings the night reserve with it (see fuel and energy planning for general aviation).

Recent experience for night passenger flights

A night rating permits night flight; carrying passengers at night also needs recent practice. Under FCL.060, a pilot carrying passengers must have made three take-offs, approaches and landings in the preceding 90 days, and for a flight at night at least one of them must have been at night as pilot flying. It counts within the three, not as a fourth, and holders of a valid instrument rating are exempt from the night element.

The FAA's night currency, 14 CFR 61.57(b), is stricter: three take-offs and three landings to a full stop in the preceding 90 days, as sole manipulator of the controls in the same category, class and, where required, type, between one hour after sunset and one hour before sunrise. Touch-and-go landings count towards day currency, except in tailwheel aeroplanes, but never towards night currency.

Aircraft lights and equipment

Under SERA.3215 every aircraft in flight at night displays its anti-collision lights and navigation lights, and an aircraft moving on the movement area at night shows its navigation lights. The FAA calls the latter position lights and requires them from sunset to sunrise. The left (port) wingtip light is red and the right (starboard) green, each showing from dead ahead through 110° to its own side; a white tail light covers the remaining 140°, 70° either side of dead astern. Red and green seen together mean an aircraft coming towards you, a red light out to your right at about your level an aircraft crossing from right to left, and a lone white light an aircraft going away (see aircraft exterior lighting).

Strobes reflecting off cloud or haze distract the crew, spoil night vision and can cause flicker vertigo, disorientation from light flickering at about 4 to 20 times a second. SERA lets the pilot switch off or dim flashing lights in that case, though the steady navigation lights stay on; 14 CFR 91.209 lets the pilot in command turn off anti-collision lights in the interest of safety.

The instrument lists grow at night. Under Part-NCO, NCO.IDE.A.120 adds gyroscopic attitude and stabilised heading instruments and a turn and slip indicator to the day VFR list. The FAA's 91.205(c) adds approved position lights, an anti-collision light system, an adequate source of electrical energy, one spare set of fuses or three of each kind accessible in flight, and a landing light if the aircraft is operated for hire. A working torch is part of every night pilot's personal equipment.

Lights also communicate. By night a pilot acknowledges a light signal from the tower by flashing the landing lights twice, or the navigation lights if no landing light is fitted. A civil land aerodrome's rotating beacon shows white flashes or white alternating with green; in the United States military airports add two quick white flashes between the green. At many US airports with no tower, or whose tower is closed at night, pilot-controlled lighting is switched on by keying the microphone on the published frequency: seven times within five seconds for the highest intensity, five for medium and three for the lowest. The lights stay on for 15 minutes from the last activation, so the AIM advises keying again before the final approach (see aerodrome lighting and visual aids).

Night vision and dark adaptation

The retina has two kinds of receptor. Cones, packed into the central fovea, give colour and fine detail but need good light. Rods, which surround the fovea, see no colour and little detail but are far more sensitive to faint light and movement. Because the fovea has no rods, the centre of the gaze becomes a night blind spot, which the FAA describes as 5 to 10° wide: a dim light stared at directly disappears. Off-centre viewing, looking slightly to one side of the object (10 to 15° in ATPL texts, 5 to 10° in FAA handbooks), puts its image on the rods. The night lookout is a scan of short movements with brief pauses, not a stare.

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Dark adaptation is chemical. In darkness the cones adapt in about 7 minutes and the rods in about 30. The FAA's AIM states that complete dark adaptation needs at least 30 minutes in total darkness, and that a moderate degree can be reached in about 20 minutes under dim red cockpit lighting. A few seconds of bright light, from apron floodlights, a torch, a strobe or lightning, destroys it and restarts the clock. Bright-light tasks such as the walk-round are therefore finished well before departure, and a pilot who must use a light closes one eye.

Red light preserves adaptation but distorts colours: red and magenta chart markings become hard or impossible to read, and focusing on nearby objects is harder. The FAA therefore recommends dim white lighting, as low as still allows the instruments and charts to be read.

The rods need a great deal of oxygen, so night vision is the first faculty to suffer from hypoxia, measurably from a cabin altitude of about 5,000 ft. The AIM recommends supplemental oxygen above 5,000 ft at night and lists carbon monoxide from smoking or exhaust, a lack of vitamin A and prolonged exposure to bright sunlight as further enemies of dark adaptation (see hypoxia and hyperventilation).

Night illusions

Vision normally overrides the balance organs; at night the visual picture is sparse and easily misread, and the illusions combine.

• Black hole approach. On an approach over unlit water or countryside towards a lit runway, with no lights or horizon in between, pilots feel higher than they are, descend early and fly a low, flat approach that can end short of the runway. The defence is vertical guidance, an ILS, a PAPI or VASI, or a check of height against distance; FAA guidance recommends a normal circuit rather than a long straight-in approach over dark terrain.
• Runway and lighting cues. A narrower or upsloping runway makes the aircraft seem high, inviting a low approach. Bright runway lights with few lights around them seem closer than they are, inviting a high approach, and a lit road can be mistaken for a runway.
• False horizon. Sloping cloud, a dark scene scattered with ground lights and stars, or a lit shoreline can be taken for the horizon. When outside cues are fragmentary, the aircraft is flown wholly on instruments.
• Autokinesis. A single static light stared at in the dark appears to move, after about 6 to 12 seconds according to FAA material. Keep the eyes moving and relate the light to other references.
• Somatogravic illusion. Strong acceleration on a take-off or go-around over dark ground or water feels like a pitch-up, and the instinctive push can fly the aircraft into the surface. Every night take-off is flown on the attitude indicator, with a known climb attitude.

Planning and flying at night

Night planning starts with the weather. Clear skies and calm wind let the ground cool, and a temperature and dew point spread of 2 to 3 °C or less that is still narrowing in the evening points to radiation fog, thickest around sunrise. A nocturnal inversion can put a stronger wind just above calm surface air, with shear on the approach.

Route and altitude follow the risk of not seeing the ground. Over mountainous terrain a sound planning minimum is 2,000 ft above the highest obstacle, on a route along valleys or airways: the SERA night VFR figure over high terrain where the State sets none, and the margin 14 CFR 91.177 applies to IFR flight in designated mountainous areas. Routes that stay near lit aerodromes keep options open for a failure: after an engine failure at night the pilot sets best glide, turns towards an aerodrome or away from built-up areas, and switches the landing light on in time to see the ground. An alternator failure calls for shedding electrical load and landing at the nearest suitable lit aerodrome while the battery still powers lights and radio. A pilot unsure of position climbs, communicates, confesses and complies; on the ground, a pilot unsure of position at an unfamiliar aerodrome stops, holds clear of the runway and tells ATC.

Fatigue matters more at night. Alertness and performance fall to their lowest in the early hours, roughly 0200 to 0600, when a long day can end with the most demanding part of the flight (see sleep and circadian rhythms). Before departure the cockpit is organised for the dark: torch, charts folded to the route, the frequencies and lighting of the destination and alternates checked, and panel lighting set low.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.