Flight 507, a Boeing 737-800 operated by Kenya Airways, crashed in the initial stage of its second leg on 5 May 2007, immediately after take-off, killing everyone on board.
According to reports, the plane tended to bank right, which the captain countered by using his control wheel. In the series of events that would follow, it was ascertained that there was a miscommunication between the two pilots and that the co-pilot hadn’t acknowledged a verbal command by the captain requesting to activate the auto-pilot.
In the 55 seconds that followed, the aircraft was piloted by neither pilot nor the autopilot. This eventually led to the aircraft increasing its bank angle from 1 degree, at the time the captain let go of the control wheel, to 34 degrees, when the bank angle warning kicked in.
By the time the captain managed to engage the autopilot, the aircraft was banking from 50 degrees to nearly 115 degrees at 2,290 ft. By this time, the aircraft was in an unrecoverable position and crashed into a mangrove swamp less than two minutes after takeoff.
Bank angle awareness
Loss of Control accidents can occur in one of the following three typical ways in which an unusual roll attitude can develop with delayed flight crew awareness:
- When the flight crew temporarily fail to scan flight instrument(s) under the assumption that the autopilot is engaged, while it may be not (as was the case above)
- When the aircraft is flown manually in poor visibility conditions and solely based on external visual references.
- When there is a malfunction of the Attitude Direct Indicator (ADI) or Artificial Horizon (AH)
In all cases though, loss of bank angle awareness should be confined to just one pilot- Pilot Monitoring (PM) while any discrepancies (if any) should be corrected by the Pilot Flying (PF).
Instances, where there has been a successful recovery, are scarce, although it is to be noted that such occurrences can happen even in a flight deck with three members.
In addition to the loss of control, excessive banking can have significant effects on the G forces that act on a human body, depending on the degree of banking.
How do G forces impact the human body?
Science defines centrifugal force as something measured in g forces, with 1 g being gravity’s effect on a person or object at or near the Earth’s surface. Therefore, a rating of 2G means the person or object is experiencing twice the effect of gravity.
Assuming you are sitting or standing on solid ground right now, you are in a 1 G environment. Earth’s standard force of gravity (G) is pushing against you as it normally does.
When planes make rapid turns, especially in the order of 90 deg or more, it creates a radial acceleration that can generate more than 6 G’s of force- or six times the force of gravity of earth. This can have serious implications for humans who are adapted to survive in a 1G environment.
In a 1 G environment, the heart generates enough blood pressure to deliver the blood above the heart and to the organs above the chest. But in a rapidly building G environment, the acceleration force is strong enough to force the blood down the legs, making it difficult or almost impossible to flow back to the heart for re-circulationDr. Swee Weng Fan, a former flight surgeon and current managing director of training at NASTAR (National Aerospace Training and Research Center)
The human body can typically withstand about 5 Gs. At about 8 or 9 G, a human typically experiences blackout or loss of consciousness.
30 degrees of banking angle is typically the limit on a commercial passenger. 45 degrees would be deemed as “uncomfortable” by most passengers as in this case the load factor increases by 50% – giving a sensation equal to 1.4-1.5 times the body weight.
Airbus Fly-by-Wire (FBW) in normal law, apparently, doesn’t allow banking exceeding 67 degrees as such a level turn would yield 2.5G – maximum for any transport category aircraft.
Types of G forces
- +Gx – Gravitational force exerted on a pilot’s body from chest to back during take-off or sudden acceleration, pushing a pilot back into their seats.
- -Gx – Force exerted from back to chest, pushing the pilot forward. This may occur during landings or forward impacts.
- Gy – A lateral gravitational force that is exerted on the pilot’s shoulders, such as during a lateral roll.
- +Gz – A gravitational force that is exerted on the vertical plane of the body, such as during recovery from a dive or the pull into an inside loop.
- -Gz – Force exerted vertically as pilots push into dives.
An upwards acceleration of about 5g is enough to overwhelm the ability of the heart to pump blood to the brain. This causes oxygen starvation and the person can experience what is called G-LOC, or G force-induced loss of consciousness.
As arterial pressure in the eyes falls, pilots may begin to experience tunnel vision, gun barrel vision, and finally grey or blackout vision. These have often been the cause of numerous military and civilian aviation disasters over the last century.
Apparently, human tolerances of negative Gs are even worse. The negative Gs, force more blood to the head, causing vessels to burst in the eye- a condition called “red out” and, eventually, the brain. An extended force as low as negative 3Gs can be deadly.
All military and acrobatic pilots, therefore, train in Anti-G Straining Manoeuvre (AGSM) – these include various breathing and muscle-tensing techniques to minimize downward blood flow and keep the brain as oxygenated as possible. Additionally, pilots must maintain strong physical fitness, wellness and nutrition to stay alert in high-G environments.
That said, limiting alcohol consumption, resting properly before the flight, and hydrating adequately for several days before flying can also help pilots with confronting extreme G-forces.