Two accidents reveal vulnerabilities in the aviation industry’s understanding of negative habit transfer, a pervasive factor on pilot performance.
Even though expertise, intense training and experience are valued assets in aviation, high-time aviators are subject to several inherent human performance limitations. Ironically, the more ingrained our in-depth training and experience has become, the more these “muscle memory” movements can become a hindrance.
While the two accidents highlighted in this article were caused in part by the pilots’ improper attempts to override the autopilot, they reveal several Achilles heels in business aviation: being simultaneously qualified in multiple aircraft and seat swapping, qualified to fly both fixed- and rotary-wing aircraft, or flying aircraft with entirely different flight management systems (FMS), all of which are common practices in business aviation.
When our previously learned habit patterns are inappropriate for our current aircraft, environment or procedures, it is called “negative habit transfer.” The role of negative habit transfer cannot be lightly disregarded. Research by Dr. James Reason, emeritus professor of psychology at University of Manchester, found that negative habit transfer increases the chances of human error by five times. Professional flight crewmembers with thousands of hours of flight experience and rigorous repetitious training in routine maneuvers have deeply ingrained habits that will be difficult to counter, especially when time pressure is short, such as a go-around. Negative habit transfer applies not only to the physical manipulation of an aircraft’s flight controls but also to the performance of procedures.
7 Fatalities From Misunderstanding the Autopilot
The first accident we’ll discuss involved a Dassault Falcon 900B operated by Olympic Airways for the Government of Greece during a flight from Athens to Bucharest, Romania, on Sept. 14, 1999.
The aircraft was flown by two experienced crewmembers. Both pilots held ATP certificates with type ratings in the Falcon 900 and Boeing 737. The 46-year-old pilot-in-command (PIC) had 8,239 flight hours, with 2,213 hr. in the Boeing 737 and 270 in the Falcon 900. He attended recurrent training in the Falcon at FlightSafety International in August 1999. The second-in-command (SIC), age 44, had 7,465 flight hours—1,209 in the Boeing 737 and 231 in the Falcon 900. He attended recurrent training in the Falcon at FlightSafety in July 1999.
Since the Falcon 900B has hydraulically powered primary flight controls, there would be no “control pressure feedback” to the pilot, unlike a flight control system driven manually through cables and pulleys. Thus, Dassault designed and installed a system that artificially provides flight control feedback. It is called an “Arthur” unit. At low airspeeds, the Arthur unit adjusts the control pressure so that low forces on the control wheel will move the elevators. As airspeed increases, the unit adjusts the flight control pressure so that more force is required to move the elevators.
When this system fails, it illuminates the “PITCH FEEL” light. This occurred on the accident flight soon after takeoff as the aircraft was accelerating through 210 kt. The flight crew consulted the “Arthur Unit Inoperative” checklist. The pitch forces may be higher or lower than normal, depending on whether the unit failed in the high-speed or low-speed position. Unfortunately, the flight crew did not adequately understand the failure because the checklist did not include information on how to determine in which position the unit had failed. One of the notes pertinent to this failure warns fight crews to avoid large displacements and rapid movements of the control surfaces to avoid inducing high load factors.
The flight crew continued the flight cruising at FL400, then upon receiving clearance to descend to FL150 the SIC placed the autopilot in the vertical speed mode, descending at 2,200 fpm. At 15,500 ft., the digital flight data recorder showed that the elevator moved very rapidly into the nose-up direction. The autopilot thereupon changed from the vertical-speed mode to the pitch-hold mode. The Romanian Civil Aviation Inspectorate’s accident report states that the most probable cause for the autopilot to switch modes was because a new altitude had been selected while the autopilot was in the altitude-capture mode.
According to the accident report, when the pilot flying (PF) noted that the autopilot indicated no change to FL150, he moved the control column gently, commanding a nose-up movement of the aircraft, probably with the intention of assisting the autopilot with its expected capture of FL150. The accident report opined that the possible explanations for the PF’s actions included a distraction by a conversation with the flight attendant or that he was using a technique appropriate for the Boeing 737-400.
The PF’s control movement is a common practice in the 737-400. Its autopilot allows the pilot to apply pressure to the yoke even when the autopilot is engaged. In a case like this, the pilot can apply some force to the yoke to help hasten the level-off at an altitude. This reverts the autopilot to the Control Wheel Steering pitch mode as long as the pressure on the control yoke doesn’t exceed a limiting threshold. Thus, in the 737, manual override will not disengage the autopilot. The autopilot will continue to maneuver the aircraft in response to any control pressures.
This is significantly different from the autopilot in the Falcon, and this generally applies to most of the autopilots in business aircraft. The autopilot counters manual movement of the elevators or ailerons. The PF’s movement of the control yoke caused the elevator to move from a 3-deg. nose-down position to a 14-deg. nose-up position. The autopilot countered the PF’s nose-up elevator input by moving the horizontal stabilizer to trim the aircraft nose-down. In response to increasing pressures needed to move the control yoke, the PF applied increasing amounts of back pressure. This reached the elevator’s servomotor torque limit, at which point the autopilot instantly disengaged, as it is designed to do.
Over the next 24 sec., the aircraft entered 10 pilot-induced oscillations (PIOs) that reached peak vertical acceleration values of +4.7G and -3.26G. The Falcon 900B’s limits are +2.6G and -1.0G.
The PF reduced power, regained control when the airspeed decreased below 240 kt., and the crew declared an emergency. ATC vectored the aircraft to Bucharest-Otopeni International Airport’s (LROP) Runway 8R. Emergency response crews found six dead passengers; five injured were transported to a hospital. One of the injured passengers died three days later. The fatal and serious injuries were all symptomatic of severe impacts with the cabin ceiling and furniture.
Besides of these grievous injuries, the aircraft’s interior exhibited horrific damage. Interior furnishings, tables and armchairs were severely damaged. The luggage compartment and aft lavatory were in great disarray with glass particles, grease, toilet paper and waste found on the inner surfaces. Several cabin floor panels were distorted.
Raising Questions About Being ‘Current and Qualified’ in More Than One Type
The accident report said one of the possible explanations for the PF’s attempt to manually override the autopilot was that he was using a technique appropriate for the Boeing 737-400, in which both pilots had received a proficiency check just months prior. Neither pilot had received a proficiency check in the Falcon.
The accident report included the following recommendations:
- The Hellenic Civil Aviation Authority (HCAA) and Olympic Airways should reconsider the policy regarding operation and maintenance of a single-airplane fleet.
- The HCAA and Olympic Airways should reconsider the policy regarding the number of pilot ratings that can be exerted at the same time.
It is significant to note that the Joint Aviation Requirements-Operations (JAR-OPS) 1.980 states, “An operator shall ensure that a flight crewmember does not operate on more than one aircraft type or variant unless the flight crewmember is competent to do so. When considering operations of more than one type or variant, an operator shall ensure that the differences and/or similarities of the airplanes concerned justify such operations.”
Next: Negative Habit Transfer, Part 2
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