Fuel selector incorrectly installed

Following work to the undercarriage, the fuel selector handle was refitted incorrectly. It was fitted 90º out of position and with one bolt missing. When the selector handle was set to the main rear tank it was in fact drawing fuel from the left-wing tank, when the selector was set to the right-wing tank, the fuel selector valve was closed. If both bolts had been fitted it would not have been possible to fit the selector handle incorrectly. Following completion of repairs to the undercarriage and a taxi test by the Approved Maintenance Organisation (AMO), the aircraft was released for flight. The same afternoon I planned to undertake a short local check flight. The engine first started ok but only ran for a short time. Thereafter It would start when primed but would not run for more than a few seconds. I called one of the AMO engineers to look at the problem; he discovered that the fuel-selector handle had been fitted incorrectly and one of the fixing bolts was missing. At first, he thought the handle had been installed in reverse and, indeed, with the selector set to the off position the engine ran. However, following further checking he realised it had been installed at 90º to the correct position. I was lucky that the left wing-tank had all but run dry during the taxiing runs in the morning, otherwise it would have done so shortly after I took off. With the fuel selector set to the main rear-tank (which was full) but in fact pulling fuel from the left wing-tank, when that tank ran dry the engine would have stopped and I would have tried to select the right tank as an alternative, but this would have resulted in turning the fuel off and a forced landing.

CAA Comment

The pilot filed an MOR which has been closed by the CAA but the AMO did not file an MOR. The CAA Safety Intelligence team were able to identify that the incident resulted from several Human Factor elements, including unclear information contained within the Aircraft Maintenance Manual (AMM) and the failure of the engineer to seek advice from a more experienced member of the maintenance team. Additionally, there were issues relating to non-recording of work, supervision failures and rushed testing post maintenance. Remedial Actions have since been implemented as required.

The Human Factors issues in this report all lined up to create an extremely dangerous situation. The fuel selector had offset mounting holes that should have prevented it being installed incorrectly. Unfortunately, its location was such that pre-flight checks would be unlikely to spot the empty bolt hole, and it was only the fact that the left wing-tank ran dry because of the previous taxiing runs that saved the day. The overriding question is, even if the engineer thought that the component was orientated correctly and a bolt was left over, why did that not raise a big red warning flag? We all know of situations away from work where the odd fastener is left over after carefully erecting Swedish flat-pack furniture, but this was a component critical to the safe and correct operation of the aircraft. Refitting or replacing components in the incorrect orientation is not new of course, and there is a danger that good aircraft design to make installation fool-proof is making us lower our guard against such errors.

In larger organisations, would this issue be less likely because they are able to provide sophisticated risk mitigation, large training budgets and a permanent Quality/Safety presence? Large organisations benefit from a Human Factors advantage: that of mentoring, coaching and advising – what one might call “Good” Peer Pressure. If you are a certifying engineer with thirty licensed colleagues, then you have thirty people to ask for assistance if needed. Equally thirty people can say “you are wrong” before you make the mistake. GA certifying engineers may be working alone and although this might be routine, risk should still be assessed and mitigation possibilities considered. Using the latest revision of the AMM (and recording the ATA Chapter and Section reference) is one mitigation against error but this defence is reduced if the AMM is less sophisticated than that of newer aircraft types. If changing a component is left to the experience and judgement of the engineer, the opportunity for error increases. If a task cannot be completed within the current duty time, even if you are absolutely certain that you will be picking up the task next shift, it is not as daft as it sounds to write yourself a handover. Five minutes of notes before packing up when you are focused on the task will be a handy aide memoir next morning. Quality Assurance has to be demonstrated as required by the regulations but Quality Control is the responsibility of the certifying engineer.

An Aircraft Maintenance Licence often leads to supervisory status but there is no exam module for man-management. Now that HF training has largely moved to Computer Based Training, is our knowledge really being refreshed? Has Safety Culture become stale? Safety Culture should be more than something only the Authority and Training focuses on – it is for all of us to support and aim to improve. Human Factors is for all of us to consider all and every day, not just on recurrent training day or on quiet days when there is time, but also on the busy days when operational, management, time and adverse peer pressures plus distractions and multi-tasking all present competing challenges.