Accident to the Issoire Aviation APM30 registered F-HHOP on 02/08/2020 at Arras Roclincourt
Rupture of left flap control, loss of control during approach, collision with ground
Before landing on runway 22 of Arras aerodrome, the screw of the left flap control on F-HHOP failed in fatigue. The pilot had set the flaps to the landing position (25°). It is probable that the green light of the flap selection unit was lit in the 25° position. It is also probable that the amber light remained off as it is designed to indicate a malfunction upstream from the flap screws. The pilot therefore had no information on the instrument panel indicating the incorrect position of the left flap. The failure of the screw led to an aerodynamic asymmetry and the induced effects, which could have led to a loss of control. The pilot did not understand what had happened, and was not able to avoid the collision with the ground at 12:53. The wreckage was situated in a field planted with tall corn, making it invisible from the ground.
The emergency locator transmitter (ELT) was effectively activated on impact. However, the distress signal was not emitted due to the connector linking the ELT to the interior antenna, fixed to the back of the pilot’s seat, having ruptured. This meant that the associated search procedures were not launched. While it is probable that the accidental rupture of the connector was prior to the accident flight, the BEA cannot rule out the possibility that the connector ruptured on impact with the ground.
Despite numerous telephone exchanges between the pilot and his former instructor, and between members of the flying club and the local rescue services (Pas-de-Calais SAMU called on 112, fire brigade called on 18), neither the members of the flying club who were looking for him nor the SMUR emergency responder team who had positioned themselves on the south side of the motorway, nor the fire brigade who had tried to retrieve the position of the pilot’s telephone, were able to accurately locate the accident. It was the Pas-de-Calais SAMU helicopter pilot who identified the accident site north of the motorway from 13:56 and then transferred the SMUR medical team who reached the pilot at 14:05, i.e. around 1 h 15 min after the accident.
The pilot was found unconscious and then declared dead.
The BEA issues 2 safety recommendations:
- Recommendation FRAN-2024-004 / Examination of screws (41) and analysis of results:
The scanning electron microscope (SEM) analyses of screw (41) on the left side of F-HHOP, carried out at the BEA, found that it had failed as a result of a fatigue cracking process under alternating bending loads. The failure of this screw is liable to result in the asymmetric extension of the flaps, the aerodynamic effects of which might compromise the controllability of the aeroplane. The asymmetric marks left by the conical washers on the left arm are consistent with a tightness fault of the screwed assembly without it being possible to determine the exact cause of this. A tightness fault can contribute to the development of a fatigue cracking process.
The SEM examinations of other screws (41) carried out by the BEA (right flap of F-HHOP and screws from two flaps of a second APM30) found micro-cracks in the root of the thread, invisible to the naked eye, in a comparable area to the failure area of the left screw of F-HHOP. The propagation of these cracks is the last step in the fatigue process before the final failure. No mark characteristic of a tightness fault was found on the arm of the right flap of F-HHOP. The arms of the second APM30 were not examined.
The final failure of the screw occurs when the aerodynamic stresses on the flap increase and the remaining stressed section of the screw is no longer sufficient to withstand the in-service loads, as may be the case when the flaps are operated by the pilot, for example during the approach or after take-off. The surprise effect which might result from this type of failure and the low height at which it might occur leave pilots little time to analyse the situation and attempt to regain control of the aeroplane.
The observation of a fatigue cracking process on each of the four screws examined by the BEA and the potentially catastrophic consequences of the failure that may result from this, as materialised by the accident to F-HHOP, call into question the level of airworthiness of the fleet made up of some thirty aeroplanes.
An AD was issued by EASA on 9 May 2023, referring to the mandatory Service Bulletin No 63 issued by Issoire Aviation on the same day. These documents mention a possible condition compromising safety. Operators are required to check screws (41) for play and replace them on all APM20s and APM30s in operation. The replaced screws must be sent to Issoire Aviation. It is specified in the AD that it has been issued on a temporary basis and that other subsequent ADs may be issued in order to implement other actions if necessary.
At the time of writing this report, neither the nature of the examinations carried out by Issoire Aviation nor their results, are known to EASA. No additional AD is planned at this stage.
Consequently, the BEA recommends that:
- whereas the left flap screw (41) on F-HHOP failed following a fatigue cracking process;
- whereas the three other APM30 flap screws (41) examined by the BEA had micro-cracks, invisible to the naked eye, testifying to a fatigue cracking process;
- whereas it has not been shown that the check for play of screws (41) is sufficient for preventing the fatigue cracking process from starting;
- whereas the failure of screw (41) can result in the asymmetric extension of the flaps and compromise the controllability of the aeroplane;
- whereas this situation is likely to occur at low height, leaving the pilot little time to recover the control of the aeroplane;
- whereas the AD published in May 2023 was an urgent, temporary measure and the ensuing results are not yet known by EASA;
- whereas it has not been shown that simply replacing the screws with identical screws, as recommended by the AD published in May 2023, means that the risk of a new failure during the service life of the aeroplane will be avoided;
EASA ensure that Issoire Aviation carry out the relevant examinations of the collected screws, and analyses of the results in order to determine whether or not the risk of failure persists, and impose new preventive measures if these prove necessary.
- Recommendation FRAN-2024-005 / Installation of emergency locator transmitter (ELT):
The investigation found that the connector linking the ELT to the antenna was ruptured on F-HHOP. The connector was probably damaged before the accident flight when a passenger took the rear seat or on positioning an object on the seat or from a harness shoulder strap, although it is not possible to rule out the possibility of the connector having ruptured on impact.
The nominal operation of the ELT and the correct transmission of the distress signal are fundamental to the satisfactory launch and coordination of search and rescue operations, even when the accident site is close to an aerodrome or the departure base of the rescue teams.
The rupture of the ELT-antenna connector which prevented the distress signal from being transmitted correctly, could probably have been avoided by protecting the ELT and its accessories.
At the time of writing this report, Issoire Aviation indicated that it had explored various installations providing effective protection of the ELT. It specified that it was also studying the possibility of using another ELT model which had a self-test which detects an antenna connection fault.
Consequently, the BEA recommends that:
- whereas the correct transmission of the ELT is an essential component for quickly launching appropriate search and rescue resources in the event of pilot incapacitation, as defined in national and departmental plans;
- whereas the physical protection of the ELT, its antenna and its cables and connectors is essential in order to preserve the chances of correct transmission by the ELT in the event of an accident;
- whereas it is probable that the connector linking the F-HHOP ELT to its antenna was torn off prior to the accident flight, on the ground, by the movement of a person or object in the rear or from a harness shoulder strap (although it is not possible to rule out the possibility of the rupture having occurred during the impact of the accident) which meant that there was no correct transmission of the ELT signal;
- whereas the information collected by the BEA during the investigation indicated that untimely ruptures of the ELT-antenna connector have been detected by other operators of APMs;
- whereas the ELT’s built-in test does not make it possible to detect a disconnection of the antenna on the Kannad AF Compact models,
EASA ensure that Issoire Aviation develop a robust solution for the installation of an ELT and its accessories on board APMs and that this solution is also implemented on the aeroplanes already in service.
The recommendation is being processed
The status of the recommendations is available at SRIS2: click here
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Note: in accordance with the provisions of Article 17.3 of Regulation No 996/2010 of the European Parliament and of the Council of 20 October 2010 on the investigation and prevention of accidents and incidents in civil aviation, a safety recommendation in no case creates a presumption of fault or liability in an accident, serious incident or incident. The recipients of safety recommendations report to the issuing authority in charge of safety investigations, on the measures taken or being studied for their implementation, as provided for in Article 18 of the aforementioned regulation.