Improper preflight inspections have contributed to several aviation incidents and accidents. The omission of a critical task, such as removing a protective pitot probe cover or engine inlet cover can have serious consequences, including death.
Examining events where an error occurs during a preflight inspection reveals that pilots of aircraft, both large and small, and of various skill and experience levels have all made these mistakes. Often these errors or omissions are the result of distractions, less-than-perfect memories, a bias, or inattention.
On Aug. 8, 2008, an MD Helicopter 369D (Hughes 500D) crashed near Alice Arm, British Columbia, killing one pilot and three passengers. It was the first flight of the day.
Before the crash, the helicopter departed in a shallow left-climbing turn, emitted an “unusual sound,” banked 90 degrees to the right, and fell to the ground from a height of 150 feet. Upon ground impact, all four occupants were killed, and the helicopter slid into the Kitsault River.
According to the Transportation Safety Board (TSB) accident report, the pilot had a lot of experience—nearly 11,000 flight hours over a career that spanned 38 years. Likewise, he was properly certified, qualified, and well-rested.
The accident site was located near a base camp and lodge where the helicopter would ferry workers to a nearby mining site. At this base camp, the helicopter operator employed a pilot and an apprentice engineer to help with “elementary tasks.” The engineer would “look over the helicopter” and secure it each night. This included installing a “doghouse cover” over the engine intake and around the main rotor control system. He would also tie down the main rotor.
The doghouse cover is red in color and made of a heavy synthetic material and is secured to the aircraft. In this case, the cover did not have any straps or physical barriers (streamers or flags) that fell below the human eye level. According to investigators, “Once the pilot gets into the helicopter, there are no visual cues of the covers installation.”
In addition to securing the helicopter each night, the engineer would prep the aircraft for flight each morning. Two days before the accident flight, the pilot would take over all the morning preflight duties, allowing the engineer to presumably get more rest. The engineer would continue to service and secure the aircraft each night.
On the morning of the crash, the pilot woke up at his normal time but was delayed leaving the lodge. Upon arrival at the helipad, the weather was clear with no wind. Two of the three passengers were already at the helipad and the pilot began his preflight activities, which included loading the equipment and gear onto the helicopter. The third passenger then arrived, more gear was loaded, everyone boarded, and the helicopter departed almost immediately.
At the crash site, investigators would find the doghouse cover tightly wrapped around the main rotor control system and swashplate. Nearly all control linkages (pitch change rods) were broken. Blade damage was consistent with low or no rotor RPM at impact. Tree damage and ground scars were representative of a near-vertical descent into the area of impact.
In its analysis, the TSB said, “It is clear that the removal of the cover was missed during flight preparation and the cover damaged the main rotor controls while the rotor was turning.” Due to the binding effect of the cover in the rotor system, rotor RPM was lost, and the helicopter became uncontrollable.
Further analysis focused on human factors and how a highly experienced pilot could miss removing the cover during preflight. The report stated, “Because humans are easily distracted and our memories are less than perfect, we use training, routine, checklists, visual cues, and physical defense barriers to help us carry out required tasks.”
Accordingly, there were no physical barriers to prevent the pilot from operating the helicopter with the cover installed. Once the pilot removed the ties from the main rotor, the physical barrier and visual cues were removed.
From the exterior, the doghouse cover was above eye level and, once seated in the cockpit, it was out of sight. Additionally, the report suggested, that there was a “lack of mental imprinting” or routine since the engineer would normally install and remove the cover. In addition, there were many other distractions during the preflight phase including briefing passengers, loading gear, and other tasks.
Following this accident, the operator and the manufacturer modified the doghouse cover to include streamers/straps that hang down from the rotor system to the front doors.
Trouble Down Under
During a recent three-year period, the Australian Transport Safety Bureau (ATSB) has investigated three serious preflight incidents involving airliners. Each investigation provides details and insights—not only of the event but to the many human factors issues that may contribute to professional pilots and support personnel missing critical items during preflight inspections.
On Sept. 22, 2021, a Qantas Boeing 787-9 completed a 14.5-hour freighter flight (a passenger aircraft transporting Covid supplies) from Melbourne to Los Angeles. Upon arrival, maintenance engineers found all four fan cowl static ports taped over with adhesive and barricade tape.
The fan cowl static ports provide redundancy to the electronic engine control (EEC) system of both engines if the primary EEC system malfunctions. Fortunately, the crew did not observe any adverse consequences during the flight.
Three months earlier, on June 21, another Qantas 787-9 performed an “air turnback” after neither of its main landing gear would retract after takeoff. Two of the five landing gear down lock pins—one on each main landing gear—had not been removed before flight.
During the initial climb, the flight crew selected the landing gear lever to “UP” and received warning messages that the main gear had not retracted. After consulting the aircraft’s electronic checklist, the flight crew was unable to resolve the landing gear issue and was forced to return to its departure airport for an uneventful landing.
Three years before these Qantas preflight incidents, on July 18, 2018, a Malaysian Airlines Airbus A330-300 failed to reject its takeoff from Brisbane despite the absence of any reliable airspeed indication for either pilot. All three pitot covers were not removed before flight.
During the initial takeoff roll, the flight instruments showed a red speed flag in place of airspeed and unrealistically low airspeed afterward. The flight crew’s actions were delayed—startle, surprise, and ineffective communications—until the aircraft’s speed was too high to reject the takeoff, and the takeoff was continued.
After troubleshooting, aircraft non-normal procedures would lead the crew to shut down the aircraft’s air data system, which activated a backup speed scale (BUSS) system to display a safe flight envelope. Using the BUSS, prescribed airspeed management procedures, and ATC assistance, the aircraft was able to return to Brisbane for a landing.
Following the Qantas 787 fan cowl static port incident, ATSB investigators attributed the oversight to inadequate preflight maintenance and operational procedures. Before departure, maintenance engineers, ground dispatch personnel, and pilots were required to inspect the aircraft before departure; this included inspecting 14 probes located on the fuselage, engine nacelles, and vertical fin. During the preflight by at least three individuals, no one found the yellow adhesive tape or red barricade tape that covered the static ports.
The second officer—the flight crewmember tasked with the preflight inspection—found one pitot probe cover on the ground and returned it to an engineer. When asked about the fan cowl static ports, he was aware of their function, but was not aware that they could be covered with tape.
ATSB Investigators noted “several missed opportunities” during the Malaysian A330 incident including procedural non-compliance by several individuals who failed to detect that all three pitot mast covers were installed before flight. Likewise, investigators were deeply concerned that the takeoff had been continued rather than rejected.
According to the ATSB report, there were five required walkaround checks required once the aircraft was parked at its stand in Brisbane. Four of those checks should have taken place after the pitot covers were installed; thus, there were multiple missed opportunities for the covers to be detected and removed.
As an example, the licensed aircraft engineer (LAE)—an employee of the airline—performing the transit check noted the pitot covers installed on the aircraft but chose to later notify another support engineer (contracted to the airline) to remove them. This was atypical since pitot covers were not normally installed by this operator at this airport during an in-transit stop. The LAE continued with the transit check tasks on the flight deck and forgot to notify the other engineer.
Human Factors Identified
ATSB identified several human factors issues with this event, including limitations such as prospective memory. Prospective memory is defined as suspending or deferring a task with the intention to return to it later or forming an intention to add a new task later. These memory failures also occur with tasks that are not habitually performed. In this case, the LAE did not routinely use or need to remove the pitot probe covers, and accordingly never used them during turnarounds.
According to the report, another reason why people forget to complete a task as intended is the absence of reminder cues. There were no cues to prompt the LAE’s memory since he was working inside the aircraft (probes and streamers were outside) and there was no entry in the aircraft technical logbook or placard in the cockpit.
Another missed opportunity was the pre-departure walkaround check—no one did it. The airline’s LAE was under the assumption that this was a task performed by the support engineer, whereas the support engineer was under the impression that his job was only to support the LAE. Had either individual conducted the pre-departure walkaround check, they most likely would have noticed that all three pitot probe covers were not removed before flight.
The ATSB report also highlighted the captain’s reduced level of attention during the preflight walkaround inspection. CCTV footage of the captain’s preflight revealed that his flashlight shined on the covered pitot probe only briefly and he omitted other items during the inspection.
ATSB also cited a phenomenon known as “inattention blindness,” where people rarely cognitively perceive what they are looking at unless attention is directed to it. Other research supports this theory and suggests that people are more likely to detect targets when they are expected and less likely to detect targets that are not expected.
Overcoming these human limitations is important—during preflight activities or even flight path monitoring, be sure to look for something, not at something. Examples: Look for the hole that the gear pin goes into or look for the pitot probe to be free from any damage, obstructions, or protective covers.
Additionally, other physical barriers or visual cues such as a placard—such as “pitot probe covers installed”—on the control yoke or throttle quadrant or maintenance logbook entry would bring attention to these covers.
Expectation bias is another limitation of the human brain. According to the report, “Expectation has an influence on perception: people see what they expect to see.” The captain reported never seeing pitot probe covers during previous walkarounds and did not expect to see them on the aircraft in Brisbane.
As identified by Canada’s TSB and Australia’s ATSB, humans are not perfect. Our memories are less than perfect; thus, we must use training, routine, checklists, visual cues, and physical defense barriers to help prevent these errors.
The opinions expressed in this column are those of the author and not necessarily endorsed by AIN Media Group.