AAIB Bulletin: 12/2024

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91 ©Crown copyright 2024 All times are U TC AAIB Bulletin: 12/2024 G-LDGB AAIB-29159 Accident Aircraft Type and Registration: Diamond DA 40 NG, G-LDGB No & Type of Engines: 1 Austro E4-A piston engine Year of Manufacture: 2015 (Serial no: 40.N296) Date & Time (UTC): 16 May 2023 at 1445 hrs Location: 3 nm north-west of Oxford Airport Type of Flight: Training Persons on Board: Crew - 2 Passengers - 1 Injuries: Crew - None Passengers - None Nature of Damage: Rear passenger door detached from airframe Commander’s Licence: Commercial Pilot’s Licence Commander’s Age: 33 years Commander’s Flying Experience: 1,700 hours (of which 500 were on type) Last 90 days - 52 hours Last 28 days - 32 hours Information Source: Aircraft Accident Report Form submitted by the pilot and further AAIB enquiries Synopsis Whilst conducting an instrument flying training lesson the rear door detached from the aircraft. The instructor inadvertently disengaged the primary locking mechanism whilst pressing the rear door handle to demonstrate to students how to secure it in the event of an in-flight Primary Flying Display (PFD) door warning. The aircraft landed safely and there were no injuries. The Operator undertook a number of safety actions following the event. History of flight The flight was an instrument flight training lesson, there was also a passenger, another student, who was to observe for local area familiarity and lesson content. Part of the Operator’s checklist for the Diamond DA40 NG requires that the rear door is to be confirmed closed before engine start and before take-off. On both occasions the student pilot and the instructor observed the student in the rear seat check that the handle mechanism of the rear door was in place and apply pressure to the door; all crew members were content the rear door was locked. Furthermore, the door warning light was confirmed to be off on the PFD as required the aircraft checklist. 92 ©Crown copyright 2024 All times are U TC AAIB Bulletin: 12/2024 G-LDGB AAIB-29159 Following a successful take-off and initial departure by the student, control was handed over to the instructor during climb out to enable the student to don the instrument flying hood1, control was then returned to the student. Prompted by a routine altitude warning and call out by the student pilot during the climb out, a discussion commenced with the instructor about visual and audio warnings on the PFD. The instructor demonstrated how selecting the pitot heat on would be displayed on the PFD. There then followed a discussion about the most common occurrence being door warnings and how these can be triggered by the door handle being open a small amount. At this point the instructor reached back and pushed on the rear door handle to demonstrate to the students how to secure the door following an in-flight PFD warning that would indicate the door was not closed. As the instructor interacted with the door handle it unexpectedly opened fully. With the student pilot still flying, the instructor and rear seat student assessed the situation. The rear seat passenger could not reach the door to close it due to the seat restraint harnesses and shortly afterwards the door fully detached from the airframe. The instructor took control of the aircraft, contacted ATC to advise of the situation and was given clearance to land. The return to the airfield, landing and taxi were uneventful and there were no injuries to the occupants. The aircraft is shown below (Figure 1). Figure 1 G-LDGB with rear door missing (image used with permission) Footnote 1 IFR Hoods or View Limiting Devices are used by pilots during flight training to simulate flying in the clouds or in poor visibility. It restricts their view so the student can only see the flight instruments, forcing them to fly without any external references to the ground or horizon. 93 ©Crown copyright 2024 All times are U TC AAIB Bulletin: 12/2024 G-LDGB AAIB-29159 Rear door description and operation The rear passenger door is a carbon fibre reinforced plastic moulding with inner and outer frames bonded together. The door has an acrylic glass window. Two hinges attach the door to the top of the fuselage near the centreline. A gas strut attaches to the rear of the door and the fuselage which holds the door open on the ground. A handle on the left of the door operates two locking bolts located at the bottom front and rear corners of the door. An additional safety latch is fitted (Figure 2). The function of this red safety latch is to hold the unlocked passenger door in a near closed position, whilst the aircraft is parked on the ground, protecting the passenger door from wind gusts. It also helps reduce the risk of a passenger door separation in case of an inadvertent opening of the door locking mechanism by a passenger during flight. Although it should be noted that the original design intent of the red safety latch was not to prevent a passenger door from separating from the aircraft because of a failure to lock the passenger door before flight. The passenger door hinge design provides a predetermined breaking point, strong enough to comply with the certification specification but allowing a passenger door, which was closed, but improperly locked, to separate cleanly from the airframe with minimal damage. If the passenger door swung open and did not separate from the fuselage, reduced controllability of the aircraft would be the consequence. Figure 2 Rear passenger door handle configuration (image used with permission) There is a DOOR OPEN warning that activates on the PFD if the primary locking mechanism is not properly located. However, there is no way of demonstrating this warning on the PFD without opening the doors. This warning can be demonstrated in the DA 40 simulator, but the operator did not have this facility. 94 ©Crown copyright 2024 All times are U TC AAIB Bulletin: 12/2024 G-LDGB AAIB-29159 Operators Investigation