During hovering practice, a student pilot applied left pedal input, but the flight instructor noticed the helicopter started to rotate toward the right. The instructor later reported that he suspected a loss of tail rotor effectiveness (LTE) and performed a hovering autorotation to land on a field. LTE is an example in which the causal conditions can quickly create a surprising and overwhelming reaction that the flight controls may not be adequate to counter.
There is a real danger when there is a mismatch between the pilot’s expectation and reality. This is especially the case when an aircraft is behaving in a sudden and threatening manner but is not responding normally to the pilot’s control inputs. The Boeing 737 Max crashes of Lion Air Flight 610 on Oct. 29, 2018, and Ethiopian Airlines Flight 302 on March 10, 2019, will long be etched in accident investigation and engineering journals as examples of this phenomenon.
Ethiopian Airlines Flight 302’s cockpit voice recorder revealed the pilots’ struggle to manually bring the airplane out of a dive by pulling back on the control yoke and turning the trim control wheel. With both pilots pulling back on the stick, the front end of the plane continued to drop, until reaching 40° nose down. The two pilots together were not strong enough to break the counter forces on the control surfaces.
Not only were these flight crews desperately fighting against insurmountable control forces, simultaneously the cockpit was erupting with multiple alarms and alerts. This included continuous control column shaking and low airspeed warnings on one side of the aircraft. The pilots received alerts warning that the computer had detected conflicting airspeed, altitude, and angle-of-attack readings.
The mental confusion caused by multiple alarms and alerts in a cockpit is a condition that manufacturers should not allow. From a human performance standpoint, it is unrealistic to expect a pilot to troubleshoot an underlying problem causing unusual aircraft motions while struggling to control an aircraft that isn’t behaving in a predictable manner.
A review of 246 Aviation Safety Reporting System (ASRS) entries involving abrupt aircraft motions following the sudden disengagement of the autopilot indicated significant temporary spatial disorientation caused by somatogravic (vestibular) illusion and adverse kinesthetic (awareness of body position and movement) feedback from the flight controls, both of which significantly compound the ability of the pilot to promptly and accurately detect and make measured deliberate control inputs. The insight from these ASRS reports helps to explain how highly experienced pilots in many loss of control events have been unable to quickly detect and react to abrupt undesired aircraft motions.
Priorities After A Surprise
No one can predict when an engine might have a compressor surge on takeoff, when an aircraft taxis across the runway during takeoff, or a flock of geese obscures the windshield. It is realistically impossible to predict and train for each and every possible situation.
Are there general principles that can apply across a spectrum of surprise events? Fortunately, our profession has been given a number of great examples to follow when faced with sudden surprises. The flight crews of the United Airlines DC-10 emergency landing at Sioux City, Iowa, the Miracle on the Hudson, and the Hawker midair collision with a glider over Carson City prioritized the three key elements that have been a cornerstone in handling an aircraft emergency.
First and always—Aviate. Everything else is secondary to getting and maintaining aircraft control. When flying a fixed-wing aircraft, David Carbaugh, Boeing’s former chief pilot of flight operations safety, recommends attaining an appropriate pitch attitude and thrust setting. How do you know the appropriate pitch attitude and thrust settings for your aircraft? You should familiarize yourself with the typical pitch and thrust settings during normal operations.
Carbaugh advises pilots to confirm suspected instrument anomalies by cross-checking with other instruments, being aware of the reliability of each instrument used for the cross-check. An aircraft’s pitch and roll attitude information is generally reliable, especially as comparators would quickly point out an discrepancies between the captain’s and first officer’s primary flight displays. An engine’s thrust setting using the N-1 gauge would also be considered a reliable source of information.
The situation for “surprise” motions in a helicopter are too numerous and complex to summarize in a few sentences. As indicated by the Mosby accident investigation, in some emergencies it is necessary for the pilot to make an immediate and accurate control input to counter the abrupt undesirable motion of the rotorcraft. It is important to note that a majority of these conditions cannot be safely replicated for training purposes in an actual helicopter. Thus, it leaves open the immense question on how the industry safely trains its pilots to handle these surprise conditions.
This author has traveled to a wide variety of training operators, literally from Switzerland to Hawaii, to sample their techniques and suggestions, and this will be reported in a future article. There simply isn’t space here to delve more into rotorcraft-specific mechanical and environmental conditions that can cause abrupt undesirable motions.
Secondly, Navigate. In other words, get pointed in a safe piece of sky. If a malfunction occurs while on departure from Aspen, stay on the escape maneuver that avoids getting any closer to the threatening terrain. If you are on the North Atlantic Track System and must begin an immediate descent due to an engine failure or loss of pressurization, follow the prescribed procedure for getting off the track to avoid causing a loss of separation with aircraft following the same track at adjacent lower altitudes.
Thirdly, Communicate. In a situation such as the initiation of an emergency descent due to a loss of pressurization, your timely communication with ATC can alert the controllers if there is an aircraft on a converging flight path with your own. In the Hawker example referenced earlier, even though the copilot couldn’t hear a thing over the roar of the airstream thrusting through a hole in the instrument panel, he still attempted to communicate the aircraft’s emergency status to ATC. This resulted in Reno Approach watching the aircraft’s emergency descent and dispatching first responders to Carson City Airport.
The Hawker flight crew deservedly joined the ranks of elite aviators as role models of how to handle a surprise. Hopefully, you will never be confronted with a glider’s wing spar smashing through your instrument panel.
Endnote: In 2007, the Flight Safety Foundation presented NetJets pilots Capt. Annette Saunders and First Officer Mitchell Merchant with the Professionalism Award for safely landing their Hawker 800XP after colliding with a glider at 16,000 ft. The award is given to crewmembers who, by relying on skill and quick thinking, display outstanding professional performance.
Handling Surprises In The Real World, Part 1: https://aviationweek.com/business-aviation/safety-ops-regulation/handli…
Handling Surprises In The Real World, Part 2: https://aviationweek.com/business-aviation/safety-ops-regulation/handli…
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