Disorientation During Vectored Go-Around (OGHFA SE)
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Revision as of 12:01, 25 October 2012 by Timo.Kouwenhoven
|Content source:||Flight Safety Foundation|
|Human Factors Aspects||Workload, Visual Confusion, Attention and Vigilance, Spatial Disorientation, Stress|
|Flight Phase||Missed Approach|
|Operator's Guide to Human Factors in Aviation|
|Disorientation During Vectored Go-Around|
The Incident as a Situational Example
You are in descent for a surveillance radar approach (SRA) to the runway. The aircraft is cleared to 1,500 ft with radar vectors to a point “XYZ” located some 9 nm south of the airport. Weather is reported as visibility 5,000 m (3.1 mi) in rain, with some clouds at 1,000 ft, scattered at 1,800 ft and broken at 3,000 ft.
Having been configured for landing, the aircraft is on a northerly heading past “XYZ” using the heading selector. The accuracy of the map display is checked and is consistent with radar information provided by air traffic control (ATC). You select a vertical descent speed of 700 fpm and an indicated airspeed of 135 kt.
As the aircraft approaches the visual decision point (VDP) at 1,000 ft, navigation (NAV) accuracy is confirmed, and you can see the runway end identifier lights (REIL) in the expected position. The first officer confirms that the runway lights are in sight when asked by ATC. You select 090 degrees on the heading selector, putting the aircraft into a right turn with a bank of 20 to 25 degrees. You then disengage the autopilot and autothrottles, deselect the flight director, maintain a steady bank and a descent rate of 700 fpm, checking that you can still see the REIL.
The first officer monitors heading selection and airspeed and preselects the tower frequency, during which he no longer sees the runway strobe lights (REIL). Neither do you.
What is your decision?
You decide on an immediate go-around and flaps 20. You apply manual go-around thrust but do not select the go-around switch on the thrust levers. The first officer advises ATC of the go-around and notes that his attitude director indicator (ADI) is not annunciating “GA.” He advises you, and you who push the go-around switch, prompting the flight directors to command a climb on the existing aircraft track.
At about that time, ATC instructs you to turn to a heading of 180 degrees, which is selected by the first officer, who notes high ground depicted on the left side of his horizontal situation indicator (HSI). A “TERRAIN” alert is displayed on the enhanced ground-proximity warning system (EGPWS).
What is your next move, in response to the terrain alert?
Once level at the minimum descent altitude, you decide to divert to another airport as you believe low clouds caused the crew to lose sight of the runway strobe lights at the intended destination.
Data, Discussion and Human Factors
Statistics show that 5 to 10 percent of all general aviation accidents can be attributed to spatial disorientation, and 90 percent of these accidents are fatal. Similarly, 21 percent of approach and landing accidents involve disorientation or visual illusion. This effect may be airfield-dependent.
The crew was qualified to operate into the airport, and both pilots had actually done so. They briefed the approach procedure and configured the aircraft correctly before the VDP. At the VDP, both crewmembers saw the runway strobe lights and confirmed this fact with ATC. At that point, they were cleared to turn and line up with the runway.
As the pilot flying, the captain then disengaged the autopilot, autothrottles and flight directors. With reduced visibility, workload management became more problematic when conducting the final approach. Whereas the captain had initially eased his task by using automation to enable early visual contact, he actually complicated matters for himself after passing the VDP.
It would have been easier for the first officer to maintain visual contact with the runway from the right seat. The first officer announced that he preset a radio frequency in anticipation of an expected change. From then on, both pilots — probably having both been looking down — lost visual contact with the runway strobe lights. These lights are necessary to help mitigate potential threats of visual confusion with limited runway lights and ambient lighting. ATC procedures require the strobe lights to be switched off when aircraft are at 2 nm unless requested differently by the pilot or if visual contact is not confirmed.
The go-around was decided on promptly, but the captain did not realize that he was turning right and right of centerline because his attention and vigilance were limited by what to do next, where to go around to, being squeezed between the risk of infringing another nation’s airspace and approaching high ground around the airport. This is where vestibular control (spatial disorientation) may have caused some further confusion as the captain thought he was maintaining a constant runway heading. The right turn was actually continued as the captain was reminded to push the go-around switch, after which the flight director bars reappeared to command the current track of about 140 degrees. ATC then instructed the crew to continue this right turn to a heading of 180 degrees to clear high ground.
As both pilots were fully absorbed by the priority of promptly executing the climb, they temporarily failed to ensure that they were on the correct missed approach track. Stress or ensuing narrowing of the attention span can often be destabilizing in such unexpected situations where imminent decision making may lead to the risk of pilot error.
However as the aircraft’s lowest altitude over land was 2,100 ft, controlled flight into terrain (CFIT) was never a real threat. The controller provided effective control by rapidly providing vectors to avoid the high ground. At go-around, the aircraft was descending through 650 ft at 134 kt, with a bank of 8 degrees to the right and through a heading of 077 degrees. It then descended a further 100 ft before actually climbing. It achieved a climb rate of 3,000 fpm while turning to a heading of 140 degrees, remaining there for 12 seconds, then turned left to a heading of 134 degrees for another 12 seconds before ATC brought it to 180 degrees, over land and at 2,100 ft.
The missed approach procedure actually calls for a climb to 3,900 ft on runway heading, and standard ATC instructions for a missed approach from the VDP are to turn onto a north-easterly heading to ensure remaining clear of the high surrounding terrain.
Prevention Strategies and Lines of Defense
The airline considers the airport to be one requiring specific briefing and crew qualification procedures. The local topography can indeed result in wind variations leading to strong turbulence and rapidly varying visibility and cloud conditions.
The approach briefing should focus briefly and concisely on the following:
- The need for maintaining visual contact with the runway strobe lights by one crewmember, which reduces his or her capacity to monitor flight instruments.
- The need to rely on automation to support task-sharing and help workload management.
- The need for a high level of concentration and for effective coordination by the crew and ATC.
- The need for being prepared for a go-around to avoid this type of occurrence.
- The need to beware of visual illusions that may exist when looking at a misleading visual scene. Disorientation can occur when there are difficulties in orientation or when there is a mismatch between the real world and what is sensed.
- The need to maintain permanent instrument scanning to counter the potential for vestibular disorientation.
- The need for the pilot to trust his instruments rather than his own senses. The pilot may fail to perceive angular motion, called the leans; with a slow rate of roll, the pilot may feel that his aircraft is still flying straight and level although the attitude indicator shows that the aircraft is, in fact, turning.
- The need to keep in mind that this distortion of sensed information can indeed have strong effects on situation assessment and decision making.
- When situational awareness is lost, as in loss of visual contact, correct go-around procedures must immediately and promptly be followed. This involves task sharing and callouts of go-around altitudes, speeds, headings and tracks, minimum safe altitudes, sector altitudes and limits.
Most aircraft require that the initial go-around be flown at constant speed and without any acceleration with one notch of 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 are followed. In general, there are no go-around procedures that require a sustained turn. Although most are standard, some go-arounds are problematic, either due to visual maneuvering or ATC intervention.
This situational example describes an approach incident caused by loss of visual contact, inadequate workload management and subsequent disorientation in a turning climb. ATC had to intervene to avoid a risk of CFIT. Before the incident, ineffective crew briefings and nonadherence to standard operating procedures (SOPs) made the crew unusually susceptible to spatial disorientation. Inadequate go-around procedures left the crew with an ambiguity as to where to go around to.
This situational example shows how difficulties with visual contact may result in a go-around that may itself induce dangerous vestibular and spatial disorientation effects. An example is the leans. With a slow rate of roll, a pilot may feel the aircraft is still flying straight and level, although the attitude indicator shows that the aircraft is indeed banking.
A go-around procedure should not contain an acceleration and continuing turn that may contribute to disorientation. Crews might suffer somatogyral (coriolis) as well as somatogravic (false climb) disorientation.
When flying to an airport that requires a special release, the arrival briefing should summarize these key points:
- Make sure you know where to go around to (being prepared for a go-around).
- Review the availability, awareness of and adherence to SOPs (discipline).
- Maintaining visual contact with the runway strobe lights must be accomplished by at least one crewmember.
- Rely on automation to support task sharing and workload management.
- Maintain a high level of concentration and effective coordination with ATC.
- Remain prepared for a go-around; if performed, beware of visual illusions that may occur.
- Maintain continuous instrument scanning to counter vestibular disorientation.
- Trust your instruments, keeping in mind that distortion of sensed information can have strong effects on situation assessment and decision making.
Associated OGHFA Material
- Situational Awareness
- Vestibular System and Illusions
- Flight Preparation and Conducting Effective Briefings
- Stress and Stress Management
- Decision-Making Training
- Situational Awareness
- Understanding Visual Illusion and Disorientations
- Managing Visual Somatogravic Illusions
- Stress Management