Controlled Flight Into Terrain (CFIT)

Controlled flight into terrain (CFIT) is an accident in which an airworthy aircraft, fully under its crew's control, is flown into the ground, water or an obstacle. The crew usually realises the danger only seconds before impact, or not at all. Nothing is wrong with the aircraft or its handling; what fails is the crew's mental picture of where the aircraft is relative to the terrain.

For many years CFIT was one of the main killers in commercial aviation, and it drove the fitting of ground proximity warning systems. It remains among the deadliest accident types because few people survive it. IATA's analysis of 2008 to 2017 found CFIT in about 6% of accidents, yet it was the second-largest fatal accident category after loss of control in flight. About two-thirds of the CFIT accidents happened during approach and landing, and turboprops accounted for 70% of them, with an accident rate of 0.47 per million sectors against 0.05 for jets.

What is CFIT

The CAST/ICAO Common Taxonomy Team, whose categories ICAO, IATA and most investigators use, defines CFIT as an "in-flight collision or near collision with terrain, water, or obstacle without indication of loss of control". Three consequences follow:

• Controlled. If the aircraft struck the ground because control was lost, after a stall, an upset or a spiral from spatial disorientation, the event is loss of control in flight (LOC-I), not CFIT (see upset prevention and recovery).
• Terrain. Water and obstacles such as masts and towers count as terrain.
• Near collision. A terrain warning followed by an escape that narrowly misses the ground is a CFIT occurrence even though nothing was hit. ICAO Annex 13 lists controlled flight into terrain only marginally avoided among its examples of serious incidents, which must be investigated.

The typical CFIT flight is descending or approaching in cloud or darkness near high ground. The crew is busy and confident of its position, and the aircraft is doing exactly what it has been told to do.

Contributing factors and threats

At the heart of almost every CFIT accident is lost situational awareness: the crew no longer knows, continuously, the aircraft's position, its height above the terrain around it, the minimum safe altitude for that position and where the flight path will take it next. The loss can be vertical, horizontal or both, and it usually builds from several small threats.

Vertical errors usually come from altimetry: a QNH set wrongly, a QFE/QNH or hPa/inHg confusion, or cold-temperature error (see altimeter settings and the guide to cold-weather altimetry). Horizontal errors come from navigation: a wrong waypoint, a map shift, or a misread clearance. Night approaches over dark ground add the black-hole illusion, which makes the pilot feel higher than the aircraft is (see spatial disorientation and visual illusions).

Minimum safe altitudes

Charts publish several minimum altitudes, and each guarantees something different. Knowing which one applies at any moment is the basic CFIT defence. The minimum safe altitudes are:

• Minimum sector altitude (MSA). Under PANS-OPS it gives at least 1,000 ft (300 m) of obstacle clearance within 25 NM (46 km) of the navaid or fix on which it is centred, sector by sector. It guarantees neither navigation signal nor radar coverage. Below it, the aircraft should be on a published procedure, under radar vectors, or with the terrain in sight.
• Minimum en-route altitude (MEA) and minimum obstruction clearance altitude (MOCA). Under FAA rules the MEA guarantees obstacle clearance and navigation signal for the whole airway segment. The MOCA guarantees obstacle clearance only, with the signal assured just within 22 NM of a VOR. Both clear obstacles by 1,000 ft, or 2,000 ft in designated mountainous areas.
• Minimum off-route altitude (MORA) and Grid MORA. Jeppesen's route MORA covers 10 NM either side of the route centreline, and the Grid MORA each latitude-longitude square of the chart. Both clear the highest terrain and obstacles by 1,000 ft where these are 5,000 ft or lower, and by 2,000 ft where they are higher. They guarantee no signal and suit drift-down or diversion planning.

Where no minimum altitude is published, the IFR minimum levels differ. EASA's SERA.5015 requires at least 1,000 ft above the highest obstacle within 8 km of the aircraft's estimated position, or 2,000 ft over high terrain or in mountainous areas. The FAA's 14 CFR 91.177 uses 1,000 ft, or 2,000 ft in designated mountainous areas, above the highest obstacle within 4 NM of the course. Under radar vectors ATC provides terrain clearance, but a clearance never relieves the pilot of responsibility for terrain avoidance.

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Approach-and-landing accidents (ALA)

An approach and landing accident (ALA) is one that occurs during the approach or landing. The category includes runway excursions, hard landings and loss of control on final as well as CFIT short of the runway, which is the deadliest variant. IATA's data put 51% of CFIT accidents in the approach phase alone.

Non-precision approaches carry much of this risk. The traditional "dive and drive" technique descends promptly to each step-down altitude and then flies level at the minimum descent altitude (MDA), looking for the runway. That keeps the aircraft low for longer, adds thrust and attitude changes, and tempts the crew below the MDA to find the lights.

The alternative is the continuous descent final approach (CDFA): the final segment of a non-precision approach flown as a continuous descent, without level-off, from at or above the final approach fix altitude to about 50 ft above the threshold or the flare point. The go-around starts at a decision altitude chosen so that the aircraft does not descend below the MDA. EASA's Air Ops rules require commercial operators to fly non-precision approaches with CDFA unless the competent authority approves another technique for a particular runway. The FAA promotes the same technique through AC 120-108. Approaches with vertical guidance, such as LNAV/VNAV and LPV (RNP approaches), remove the problem at source; in 2010 ICAO Assembly Resolution A37-11 urged States to provide them for all instrument runway ends.

The companion defence is the stabilised approach. The Flight Safety Foundation's criteria require the aircraft to be stabilised by 1,000 ft above aerodrome elevation in IMC and 500 ft in VMC. That means on the correct lateral and vertical path, in landing configuration, at a speed between VREF and VREF + 20 kt, with a sink rate of no more than 1,000 ft/min and suitable thrust. On an ILS the aircraft must be within one dot of the localiser and glide slope. An approach that is not stabilised at the gate, or becomes unstabilised below it, requires an immediate go-around.

ALAR prevention strategies

In the late 1990s the Flight Safety Foundation led an international task force on approach-and-landing accident reduction (ALAR), which studied ALAs and CFIT accidents and published conclusions and recommendations. Its ALAR Tool Kit turned them into briefing notes, videos and presentations for airlines, training organisations, air traffic services and regulators. The main themes are:

• Procedures: clear standard operating procedures with standard calls, a defined stabilised approach policy and a go-around decision that attracts no blame.
• Approach design and technique: constant-angle non-precision approaches, vertical guidance wherever available, and precision approaches at more runways.
• Briefing and awareness: an approach briefing that covers the MSA, the highest terrain, the minima and the missed approach, supported by the terrain display.
• Altimetry: altimeter setting cross-checks, radio altimeter callouts and cold-temperature corrections.
• Communication: standard phraseology, full readbacks, and questioning any clearance that conflicts with the crew's picture of the terrain.
• Equipment and training: terrain awareness and warning systems in every aircraft, current databases and regular practice of the escape manoeuvre.

The Foundation also published a CFIT checklist, a scoring sheet with which an operator or crew can assess the terrain risk of a flight before it happens. Much of the Tool Kit comes down to crew resource management: the pilot monitoring must be willing and expected to challenge a descent that does not match the chart.

Terrain awareness and warnings

When every other defence has failed, warning systems give the last chance. A ground proximity warning system reacts to radio altitude, descent rate and configuration. A terrain awareness and warning system (TAWS) such as EGPWS adds a terrain and obstacle database that looks ahead of the aircraft, typically giving a caution 40 to 60 seconds before a potential impact and a warning 20 to 30 seconds before. Their modes, displays and carriage rules are described in GPWS and TAWS.

Three rules matter for CFIT. The terrain display is for awareness, not navigation. A database is only as good as its coverage and the aircraft's position accuracy. And a warning is never inhibited on the assumption that it is false.

On the ground, radar systems with a minimum safe altitude warning (MSAW) alert the controller when an aircraft is, or is predicted to be, below a safe altitude. FAA controllers then transmit "low altitude alert, check your altitude immediately". Crews should treat such a call as they would a terrain warning.

Terrain escape manoeuvre

The terrain avoidance manoeuvre, also called the terrain escape manoeuvre or pull-up manoeuvre, is the maximum-performance climb flown after a PULL UP warning, or after a caution at night or in IMC where the operator requires it. It is flown immediately, from memory, without first diagnosing the alert:

1. Disconnect the autopilot and autothrottle as the type procedure requires.
2. Apply maximum or take-off/go-around thrust.
3. Roll wings level, since bank reduces the climb gradient, and pitch up firmly to the attitude the type specifies (on Boeing types typically 20° initially, then towards the pitch limit indicator or stick shaker; on Airbus fly-by-wire types full back stick).
4. Retract the speedbrakes and do not change the gear or flap configuration until terrain clearance is assured.
5. Climb until the warning stops and the aircraft is above the minimum safe altitude, then tell ATC.

The detail is type-specific and practised in the simulator. American Airlines Flight 965 near Cali showed why it matters: the crew began the escape, but the speedbrakes remained extended and cost climb performance.

Lessons from accidents

Each accident combined several of the threats above, and in each a single barrier, a cross-check, a challenge, a stabilised profile or a respected warning, would have broken the chain.

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.