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Spatial Disorientation (OGHFA SE)
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|Content source:||Flight Safety Foundation|
|Operator's Guide to Human Factors in Aviation|
Human Factors Aspects: Vestibular System Illusions, Task Sharing, Coordination
Flight Phase: Approach
The Accident as a Situational example
During a visual approach at night and in visual meteorological conditions (VMC) to an airport surrounded by water, you, as first officer, have a very good view of the airport and adjacent land. On the captain’s side, it is completely dark; at night over the sea, there are no horizon cues. You see you are too high and too fast, typical of a non-stabilized approach.
- Faced with a non-stabilized approach, what would you do?
The captain, as pilot flying (PF), requests clearance from air traffic control (ATC) for a 360-degree left turn to realign with the runway. This is in violation of standard operating procedures (SOPs), but he does not want to go around. The ATC controller authorizes the maneuver.
During the tight 360-degree left turn, final preparation for landing is performed — gear and flaps fully extended, landing checklist completed. However, the airplane overshoots the runway. The captain decides to reject the landing and engages full TOGA (takeoff/go-around) thrust, delivering a constant acceleration with a 9-degree nose-up pitch attitude. The controller clears you to climb to 2,500 ft to prepare for another approach. You retract the landing gear.
During the tight turn at low altitude over the sea at night, all visual cues are lost, and both of you concentrate on the external view to reacquire situational awareness.
In a constant acceleration environment provided by the TOGA thrust, the captain turns his head to look outside, trying to get an external cue, while the airplane is pitching up.
Passing over the runway at around 1,000 ft and 191 kt, the aural master warning sounds to indicate a flap-overspeed condition.
- Would this aural warning attract your attention to a flap-overspeed situation?
After the alarm sounds, the captain pushes the controls forward. During this time, the airplane pitch attitude decreases, and the airspeed increases from about 193 kt to 234 kt.
A single aural “SINK RATE” warning is issued by the ground-proximity warning system (GPWS), followed by a repetitive GPWS aural “WHOOP, WHOOP, PULL UP” warning.
The captain requests “flaps up,” moves the controls aft of neutral and then calls for “flaps all the way.” You respond and acknowledge “flaps zero.”
The airplane is destroyed as it hits the water in a 6-degree nose-down pitch attitude at an airspeed of about 282 kt.
Data, Discussion and Human Factors
The accident report showed there was not a single cause to this accident, but several combined contributing factors led to the fatal outcome. Those factors are summarized below for the sake of completeness, and this situational example will focus on human factors issues such as the disorientation that led the captain to perceive wrongly that the airplane was pitching up and consequently led him to command and maintain a pitch-down attitude.
- Nonadherence to standard operating procedures (SOPs). The captain, as PF, did not follow airline procedures, resulting in the following:
- A higher than standard speed for start of descent and initial approach;
- A non-stabilized approach;
- The low-altitude orbit as a nonstandard maneuver to the runway; and,
- The incorrectly performed go-around.
- The first officer did not object or call the captain’s attention to his nonadherence to the procedure.
- The controller allowed a shortcut — a 360-degree turn above the airport — and did not follow the procedure for the path leading to a stabilized approach from the final fix.
- During go-around, the crew apparently experienced spatial disorientation, which may have caused the captain to wrongly think the airplane was pitching up.
- Despite the GPWS warnings, the crew did not adequately respond.
- Analysis of the cockpit voice recorder (CVR) data showed the crew did not perform as a team, due to inadequate airline training in crew resource management (CRM), SOPs, controlled flight into terrain (CFIT) and GPWS.
Disorientation: somatogravic illusion
During the approach in night conditions, the crew had on one side a very bright view of the airport and a landmass, and on the other side a completely dark area over the water.
Focusing on the visual approach, the crew may have lost visual cues and may have experienced visual illusions and disorientation when initiating the tight 360-degree turn over water, after the non-stabilized approach.
The first officer, as pilot not flying (PNF), was not monitoring his instruments and did not use proper CRM techniques to gain the captain’s attention.
In addition, TOGA provides constant acceleration. In the absence of visual cues such as the horizon, this constant longitudinal acceleration fooled the captain’s vestibular system into interpreting this as horizontal flight at constant speed.
The otholitic hairs in the vestibular system of the inner ear contribute to informing the brain of movements and orientation. They send the same signal when subject to constant longitudinal acceleration or to upward motion — or likewise when subject to deceleration and downward motion. An example is the leans: with a slow roll rate, a pilot may perceive the aircraft as still flying straight and level although the attitude indicator shows the aircraft to be, in fact, banking.
Involved in a tight climbing turn, the pilot, when turning his head, may also have been subject to the coriolis effect, which led to a loss of spatial orientation and to vertigo.
Subject to a “false climb” interpretation, the captain reacted by pushing the control column forward and maintaining the nose-down pitch attitude until he started to realize the reality of the situation. By then, it was too late due to the airplane’s low altitude.
Prevention Strategies and Lines of Defense
The first precaution to avoid an accident is to not put oneself in a nonstandard situation. The resulting situation may not appear to be risky at the beginning, but, as we know, accidents often result from multiple contributing factors. Allowing the situation to develop in the first place generates unnecessary risks.
Further, the quality of the approach briefing helps to focus on the following:
- Ensuring that one crewmember maintains visual contact with the runway lights.
- Task sharing and workload management between the crewmembers.
- Effective coordination with ATC.
- Being prepared for a go-around.
- Remembering the consequences of visual illusions when there is a mismatch between the real world and what is sensed.
- Maintaining continuous instrument monitoring to counter the onset of vestibular system illusions.
- Relying on the instruments and not on one’s own sensations; the pilot may fail to perceive angular motion (the leans); with a slow rate of roll, the pilot may feel the aircraft is still flying straight and level although the attitude indicator shows it is, in fact, banking.
- When realizing that situational awareness is lost, applying strict SOPs such as precise go-around procedures with task sharing, callouts, go-around altitudes, speeds, headings and minimum safe altitudes.
Quality of briefings
Operational procedures require a go-around to be flown at constant speed and without any acceleration with one flap retraction. The acceleration and cleanup should be done at a higher altitude. This is to ensure that a correct go-around is performed and associated procedures follow.
In general, there are no go-around procedures that require a sustained turn because, from a human factors point of view, crews might suffer somatogyral (coriolis) disorientation as well as somatogravic (false climb) disorientation.
Avoiding shortcuts and strict adherence to procedures help to avoid creating risky situations. This is the principal reason for approved SOPs.
Adherence to SOPs
Adequate CRM training helps to achieve an effective balance among crewmembers. Emphasis on cross-checking and clear task sharing provides a basis for sound attitudes. In our example, the first officer’s task was to monitor the instruments to effectively and adequately inform his captain. The captain’s role in relation to his first officer was to encourage him to speak.
Improved training in CRM and visual illusions
Training to prevent somatogravic illusion is almost impossible, but information and sensitization can help pilots recognize its onset and prepare to face it.
The only known way to regain proper orientation is to focus on the airplane’s instruments to rebuild a correct mental image of the situation.
- Discipline helps: adherence to SOPs helps improve safety.
- Constant longitudinal acceleration may generate sensory illusion.
- In the absence of visual cues, referring to the instruments to get a correct mental image and continuous instrument monitoring may help to counter vestibular disorientation.
- Adequate crew communication is a critical contributing factor to risk reduction as well as effective coordination with ATC.
- Remain prepared for a go-around while remaining aware of possible visual illusions.
Associated OGHFA Material
- Vestibular System and Illusions
- Crew Resource Management
- Adherence to SOPs
- Flight Preparation and Conducting Effective Briefings