Accident Recovery: Caught in a Jam Unsecured iPad causes deadly loss of control. By David Jack Kenny In the fixed-wing world, “sterile cockpit” refers to the discipline of refraining from all nonessential actions and communications during critical phases of flight, usually defined as ground operations, takeoff, climb, approach, and landing. Airline crews are typically required to maintain a sterile cockpit below 10,000 ft. Rotorcraft, of course, rarely see altitudes above 10,000 ft. outside of mountain rescues—but there’s an argument to be made that at low altitudes, all phases of flight are potentially critical. An alternative definition of the sterile cockpit—keeping it free of extraneous items that could cause distraction, or worse—also bears considering. An aerial view of the accident site. (NTSB Photo) The Mission On Jul. 19, 2022, a Columbia Helicopters CH-47D (Chinook) flown under contract to the US Forest Service (USFS) arrived at a helibase near Salmon, Idaho, to conduct water drops on the Moose Fire, a rapidly expanding blaze on the south side of the Salmon River that was ignited by an unextinguished campfire. Fire-suppression flights began the following day, using a 2,600-gal. bucket on a 200-ft. longline to dip water from the river, and continued on Jul. 21. The Aircraft The accident helicopter, N388RA, was originally manufactured by Boeing in 1972 and delivered to the US Army as a CH-47C. In 1988, it was remanufactured as a CH-47D; the army accepted it in 1989. The aircraft was sold to Columbia Helicopters in 2014 in a US General Services Administration auction, and then, in 2022, it was overhauled again. ROTAK Helicopter Services accepted delivery of the aircraft on Jun. 5, 2022, with a total airframe time of 7,666.4 hours and zero hours Hobbs time. The Chinook had flown another 69.5 hours as of Jul. 20, 2022. The CH-47D uses a pair of Honeywell T55-GA-714A turboshaft engines, each rated for 4,777 shaft horsepower, to drive two fully articulated three-bladed main rotors mounted fore and aft. Seen from above, the forward rotor rotates counterclockwise and the aft rotates clockwise, thus neutralizing torque reaction and providing yaw as well as pitch-and-roll control without need for a tail rotor. The aircraft was rated for a maximum gross weight of 50,000 lb. and was type certificated in the restricted category with operating certificates for Parts 133 (external load), 135 (on-demand air taxi), and 137 (aerial application). The CH-47D hovers above the river before the accident. (NTSB/Witness Video) The Crew Both pilots held commercial certificates for rotorcraft helicopter with instrument and instrument instructor ratings. The 41-year-old pilot was also rated in both single- and multi-engine airplanes. He claimed a total of 5,120 hours of flight experience, of which 4,015 were in the CH-47 or its civilian counterpart, the Boeing BV234. The pilot had completed vertical reference and external-load proficiency checks on Jun. 27, 2022, using a 200-ft. longline “and was approved to conduct Class A, B, and C external loads in a CH-47D helicopter.” He had also “demonstrated proficiency … [in] Part 137 firefighting operations in the CH-47D.” The 36-year-old copilot had 1,727 hours of flight experience. He began second-in-command (SIC) training in the CH-47D on Feb. 27, 2022, and had logged 6.6 hours as pilot in command during training and positioning flights. On Jul. 20 and 21, he logged 5.0 hours as SIC. The Flight The dip site was only about a quarter mile from the section of the fire the crew had been assigned to work, enabling them to make numerous drops in 1.5 hours of flight time. At about 16:42 local time, a local resident recorded a 38-second video clip of the helicopter establishing a 200-ft. hover over the river with the empty bucket swinging close to the water’s surface. It abruptly climbed about 125 ft. in 8 to 9 seconds while maintaining a relatively steady heading, then yawed to the left. After turning about 180 degrees, the aircraft pitched down, with the left yaw accelerating until the helicopter crashed into the riverbank and the water. USFS firefighters on the scene saw the accident and rescued the pilots. They were rushed to nearby hospitals but subsequently died of their injuries. Both deaths were attributed to “multiple blunt-force injuries”; toxicology tests were negative. The Investigation The final accident report from the US National Transportation Safety Board (NTSB) describes the organization’s examination of the wreckage in considerable detail. Item by item, they eliminated possible causes of mechanical failure throughout the flight-control system. Various fractures of control rods were consistent with impact damage, while the associated bell cranks “moved freely and were not seized.” All four integrated lower control actuators remained in their normal locations, and the mechanical connections between their outputs and the first-stage mixing unit were intact. Both mixing units remained installed, and the control rods connecting them were intact except for the left yaw/right roll rod, which had fractured in overload. The pressure-side expansion plugs had been blown out of the aft swiveling upper boost actuators, but this was attributed to ground impact forces. One puzzling anomaly provided a clue, however. The pilot’s antitorque pedals were present but had disconnected from their respective pedal position-adjustment plates, so that moving the pedals did not move the corresponding jackshafts. The right pedal position lever “had moved beyond its limit and was pointed left.” The copilot’s pedals remained attached to their position-adjustment plates, and the right pedal was adjusted to the “3,” or middle, position, consistent with the copilot’s height. The left pedal, however, was in the “5,” or full-forward, position. During the recovery of the wreckage, the crew’s company-issued Apple iPad was found in the river. Three distinct gouges had been cut into one of the long sides of the device, and the case was bent from the back toward the screen. Using an identically configured CH-47D, investigators found that if an iPad was put between the copilot’s left pedal and the airframe next to the heel slide support assembly, operation of the pilot’s left pedal caused the iPad to fall farther and become jammed between the copilot’s left pedal and the heel slide support assembly. Application of the pilot’s right pedal squeezed the iPad between the pedal and the support assembly; a sharp vertical metal piece on the bottom of that assembly aligned with the gouges in the recovered iPad. Right pedal input by the pilot “forced the iPad to apply more pressure to the copilot’s pedal adjustment lever.” With their restraints fastened, neither pilot would have been able to reach it. A Boeing simulation study found that although only 50% pedal input would be needed for the initial 180-degree left turn, full left pedal would be required to produce the yaw angle seen in the last three seconds before the crash. These findings led investigators to conclude that while the flight crew set up for the dip, the “unsecured iPad” fell under the copilot’s left pedal and got jammed between the pedal and the airframe, preventing the pedals from returning to neutral. The sudden downward pitch may have resulted from the copilot accidentally bumping the cyclic as he leaned forward to try to remove the iPad. The pilot probably reduced thrust in an attempt to slow the helicopter’s rotation, which allowed the helicopter to continue descending, and his efforts to help free the iPad by applying additional pedal pressure allowed it to slip farther out of reach while accelerating the yaw. Probable cause was therefore found to be: The failure of the flight crew to properly secure a company-issued iPad, leading to its migration into and jamming of the copilot’s left pedal, preventing the pilot from arresting a left yaw, and resulting in a loss of control. The operator confirmed that there was no reason for the crew to have used the iPad during this flight. The copilot should have been monitoring the cargo-hook load gauge during the pickup, but, based on the NTSB reconstruction of the damage to the tablet, it seems highly likely that he was also holding the tablet in his hands, precipitating the accident sequence when the device somehow slipped from his grasp. The Takeaway The version of ROTAK’s company operations manual in effect at the time of the accident placed strict limits on in-cockpit use of portable electronic devices (PED): The use of mobile phones and PED for company personnel is strictly prohibited during critical phases of flight, ground operations, maintenance, and vehicle operations. Exceptions to this can be made for emergencies that require immediate communication and when utilization of the device is critical to the task being performed. Whether the copilot was actively using the iPad or just holding it, the NTSB report notes that “the security of all items in the cockpit during an operation is necessary to ensure that they do not adversely interact with critical systems, such as flight controls.” The risk of pilot distraction posed by portable electronics has been increasingly obvious for decades, but solid objects left loose in the cockpit can also cause interference of a much more tangible kind. David Jack Kenny is a fixed-wing ATP with commercial privileges for helicopter.
