Description

Loss of control in flight (LOC-I) has been one of the most significant causes of fatal aircraft accidents for many years and is one of five global high-risk categories of occurrence identified by the International Civil Aviation Organization (ICAO). Loss of control usually occurs because the aircraft enters a flight regime which is outside its normal envelope, usually, but not always at a high rate, thereby introducing an element of surprise for the flight crew involved.

Causes

The causes of in flight Loss of Control, whether transitory or terminal, are many and include:

• loss of Situational Awareness (especially through Distraction but also through Complacency),
• Low level wind shear or higher level Clear Air Turbulence (CAT),
• Structural or multiple power plant damage caused by, for example, by a Bird Strike, exposure to severe Turbulence, or collision with another aircraft.
• Intended or unintended mishandling of the aircraft,
• Attempted flight with total load or load distribution outside of safe limits
• Unintentional mismanagement of Aircraft Pressurisation Systems,
• An attempt to take off without ensuring that critical parts of the the airframe are (or will be at rotation) free of both frozen deposits and previously applied ground de/anti-icing fluids
• The effects of high levels of airframe ice accumulation or a significant loss of power on all engines attributable to engine icing,
• Attempting to manoeuvre an aircraft outside its capabilities to resolve a prior problem (including mis-navigation).
• Fire in the Air
• Fuel exhaustion or starvation
• False instrument readings displayed to the flight crew
• Wake turbulence, especially if recommended spacing is not maintained
• Pilot Induced Oscillation
• Malicious interference

In-flight Loss of Control is (2007) the biggest single cause of transport aircraft fatal accidents and hull losses. More attention to recovery from unusual attitudes for larger aircraft operating without a visual horizon reference is also needed, since a significant proportion of airborne loss of control accidents still occur when, if recognition of an abnormal aircraft attitude had been followed promptly by the optimum recovery action, a fatal outcome could still have been avoided.

The ‘Loss of Control’ issue for light aircraft is much more focused on marginal VFR weather and associated ‘press-on-itis’ and 'get-home-itis’ and on the consequences of operating aircraft which are not certificated for flight in icing conditions in such conditions, both intentionally and unintentionally. Light aircraft pilots not adequately trained in instrument flight who end up in conditions which require it may also end up unable to retain aircraft control until a visual horizon can be re-acquired.

Categorisation

It can be useful to categorise airborne loss of control occurrences and one way to do this is as follows. The categories chosen are not necessarily independent of each other in all instances.

Significant Systems or Systems Control Failure

A significant systems or systems control failure, which interferes with normal flight management and/or directly with aircraft control may lead to loss of control. This would include multiple engine failure, loss of correct function or control of a significant element of the flying controls, especially asymmetric spoilers/slats/flaps/thrust reversers, major electrical failure and loss or malfunction of critical flight instrument displays.

Structural Failure and/or Loss of Power

The secondary result of structural failure and/or loss of power arising from a range of circumstances including mid air collision, explosive decompression, fire on board or a wing fire, and contaminated or otherwise abnormal engine fuel feed may all lead to loss of control.

Crew Incapacitation

Pilot Incapacitation such that neither pilot is able to maintain control the aircraft may lead to loss of control. This would include smoke and/or fumes in the flight deck and malfunction or incorrect control of the pressurisation system. It might also occasionally include the consequences of a deterioration in the physical or mental condition of just one of the pilots.

Flight Management or Control Error

Loss of control may occur as a result of a flight management or control error or inappropriate intervention by or under the supervision of one or both of the pilots. This would include incorrect aircraft performance calculations, unintentional pilot mis-management of critical systems including engines autopilot and fuel transfer, fuel exhaustion, pre-flight fuel loading, pilot dis-orientation under IMC or night VMC conditions and unintended operation outside the requirements of the AFM. It particularly also includes inappropriate or absent responses or inattention to otherwise relatively minor abnormalities which would not normally prejudice the safety of` an aircraft.

Environmental Factors

Environmental factors external to the aircraft which interfere with normal use of engines, flight controls or critical flight instruments or lead to their capability being exceeded or cause other serious damage, can lead to loss of control. This would include Ice accretion on the airframe or sensors before take off or during flight, microburst/severe wind shear, severe wake vortex, severe air turbulence, the effects of ice entering or otherwise accreting within the engines and the effect on multiple engine function of passage through volcanic ash or an encounter with flocking birds resulting in bird strike. It could also include the effects of damage caused by runway surface debris (FOD) of any origin which did not become apparent until after V₁.

Aircraft Load

Loading is, or becomes, contrary to the limits of the allowable flight envelope or any restrictions on what can be loaded have been breached.

Loss of control can occur if the aircraft is loaded for flight in such way that it is outside of the flight envelope or is mis-trimmed because the actual loading of the aircraft is not as documented. Flight outside the flight envelope may also arise after take off because of in-flight load shift or fuel transfer effects.

Malicious Interference

Sadly, there have been incidents in recent years when Malicious Interference with a flight by persons on board, unaccompanied explosives or external attack led to loss of control because of loss of aircraft structural integrity or direct interference with aircraft control.

Effects

The effects of loss of control may include:

• Discomfort or injury to the occupants prior to recovery to controlled flight.
• Structural damage to, or total loss of, the aircraft.
• Fatal or serious injury to occupants due to terrain impact and/or post impact fire.

The effects of loss of control depend on the ability of the pilots to recover from the situation. This, in turn, depends on:

• The nature of the upset causing loss of control;
• The experience and ability of the pilots; and,
• The height of the aircraft being adequate.

Contributory Factors

• Distraction
• Adverse weather
• Complacency
• Inadequate SOPs for effective flight management
• Insufficient height above terrain for recovery
• Lack of awareness of or competence in procedures for recovery from unusual aircraft attitudes
• Inappropriate flight control inputs in response to a sudden awareness of an abnormal bank angle

Typical Scenarios

• VFR single engine aircraft on a cross country flight has failed to check the weather forecast and plan en route alternates. When a lowering cloud base is encountered, continued flight is initially made in hilly terrain but by the time the decision to turn back is made, there is hardly sufficient space to carry out a 180 degree turn in the valley and when the aircraft is stalled inadvertently, the necessary height to recover is not available.
• The holds of a freight aircraft are incorrectly loaded. The error is not noticed before flight and when the trailing edge wing flaps are lowered during final approach the aircraft rapidly pitches up and stalls with no height to achieve a recovery.
• When fumes of uncertain origin (but with no evidence of on board fire) begin to be emitted from the air conditioning system during the cruise, the pilots fail to don their oxygen masks before both become partially incapacitated and as a result end up mismanaging the autopilot inputs so that the aircraft enters a steep dive from which, in their debilitated condition, they cannot recover.
• Whilst using a quiet time in the cruise to investigate a minor INS fault which involves changing the selected INS system, the pilots fail to note that their planned action will cause autopilot disconnection and when it does, they fail to hear the disconnect alert. Since they are both heads down, they then fail to notice a slowly increasing bank angle and heading change until the attitude of the aircraft is extreme and recovery is not achieved.
• Pitch control is lost en route and the aircraft crashes. The cause is subsequently found to have been maintenance error during a routine ’heavy’ maintenance input two days earlier
• Severe weather is entered at night during the cruise with the autopilot engaged; the rate of airframe ice build up is not monitored with the result that there is a sudden autopilot disconnect into uncontrolled flight from which recovery is not achieved before terrain impact.
• After the sudden onset of abnormal engine vibration on a twin engine jet transport, thrust on the wrong engine is reduced but as the aircraft then begins a descent, the vibration reduces anyway and it appears to the pilots that their action has had the expected effect. On final approach, thrust is required again as flaps and landing gear are lowered and increased thrust on the faulty engine is selected, resulting in premature descent into the terrain below when no usable thrust is available.
• The pilot of a piston-engine light aircraft fails to select hot air for the carburettor when descending with low power set on a warm summer day with high relative humidity; as a result, the carburettor air intake becomes blocked with ice and the engine stops. The terrain available for the necessary forced landing is very inhospitable and the result is a crash and post-impact fire.
• After take off in a multi engine transport aircraft, the PF copilot calls for ‘landing gear up’ but the PNF selects flaps up instead and neither pilot notices. As the flaps reach the ‘up’ position, the trigger criteria for stall warning changes and a warning is generated. Instead of immediately following the prescribed recovery drill, the pilots begin discussing why the warning has occurred and a full stall occurs for which there is insufficient recovery height above the rising terrain below.

Solutions

• Aircraft Unusual Attitude Recovery Training in all Full Flight Simulator Type Conversion and Recurrent Training programmes
• Multi crew pilot training which stresses the need for an effective monitoring role for the "Pilot Not Flying" (PNF) (nowadays called by some the "Pilot Monitoring" (PM) to reflect a key focus of their duties) and any other members of the flight crew.
• Pilot training which stresses the need to avoid distraction from the primary task of managing or flying the aircraft, especially when dealing with in-flight abnormal or emergency conditions.
• Pilot training and procedures which ensure that the necessary responses to imminent loss of control alerts such as stall ident/warning, bank angle and negative wind shear are followed promptly and fully.
• Continued training emphasis on VFR pilots planning and conducting their flight to stay in VMC.
• Better pre-departure access for General Aviation pilots from small aerodromes or private strips to the latest en route weather information - increase use of online methods
• A mandate to fit bank angle alerting systems to all multi engine aircraft

Further Reading

• "Applying Take-off Thrust On Unsuitable Pavement Surface May Have Hidden Dangers" looks at the situation where an aircraft can suffer structural damage from debris thrown up by jet efflux/prop wash
• "Some Thoughts on Reducing the Risk of Aircraft Loss of Control" a paper by Don Bateman for the Flight Safety Foundation (FSF) EASS 2011.
• ICAO Amendment No.3 to PANS-TRG (Doc 9868) - Chapter 7, Upset Prevention and Recovery Training, April 2014.
• FAA AC 120-111 Upset Prevention and Recovery Training, January 2017.
• Aircraft Loss-of-Control Accident Analysis, C. Belcastro and J. Foster, NASA, 2010.
• Loss of Control Prevention and Recovery: Onboard Guidance, Control, and Systems Technologies, C. Belcastro, NASA, 2012.
• Aircraft Loss of Control: Causal Factors and Mitigation Challenges, by S. R. Jacobson, NASA, 2010.

NTSB Safety Alerts on General Aviation risks related to loss of control

• Safety Alert 19 - Prevent Aerodynamic Stalls at Low Altitude
• Safety Alert 20 - Reduced Visual References Require Vigilance
• Safety Alert 23 - Pilots: Manage Risks to Ensure Safety

UK CAA

• Monitoring Matters: Guidance on the development of Pilot Monitoring Skills, CAA Paper 2013/02.