Approximately $6 billion is lost per year in the airline industry due to an Aircraft on Ground (AOG) situation. Every minute an aircraft is idle on the ground awaiting repairs, it’s haemorrhaging money for its owner or operator and causing a serious back-up of passengers across the world missing important meetings, family occasions and holidays. Aircraft have extensive and tightly regulated maintenance programmes, but when a plane such as a Boeing 747-8 comprises 6 million components (according to Lufthansa) there will inevitably be occasions when unscheduled technical faults occur. So, what are the most common technical faults which cause an AOG delay, and how long does it take to fix them?
There’s a sliding scale in terms of the seriousness of an aircraft malfunction, from post-inspection failure to instrument failure to critical issues such as sudden cabin decompression, landing gear failure or engine failure. In the vast majority of these cases, potential faults are discovered before they become an issue, during normal maintenance. Aircraft are required to undergo regulatory inspections every six to eight months and between every 400 to 600 hours. In the event of a mechanical fault happening mid-flight, a skilled crew should still be able to bring the plane down safely for repairs to be carried out. Whatever the situation in which a fault becomes apparent, however, the aircraft is immediately grounded.
Many mechanical issues are fairly basic and easily corrected. Most manufacturers of components for aeroplanes have thorough diagnostic routines to enable mechanics to identify issues rapidly and methodically.
Landing gear extension and retraction failure happens twice as often as engine problems on commercial aircraft. It can be due to low temperatures freezing the gear into the retracted position or being jammed by inadequate lubrication and an excess of dust or sand in the mechanism.
Hydraulic leaks are another scenario which should be picked up in inspections. Hydraulics are used in landing gear, brakes and flaps, and in spoilers, thrust reversers and flight controls.
Damage to an aircraft frequently occurs while it’s on the ground, for example, during loading and unloading. A surprisingly large number of events involve airbridges during connection to the plane, which can cause damage to the fuselage, the engines, and particularly the doors and door seals. Parking an aircraft can result in damage to the wing tips, especially when they’re not visible from the flight deck, which can affect the ailerons.
Water drainage and moisture control systems can cause problems, especially in the winter. When the aircraft is descending, frost melts quickly if the aeroplane skin temperature rises above freezing. This results in a sudden onset of drainage, which can end up making its way into the top (attic) of the aeroplane and then dripping onto passengers from the cabin roof – known as ‘rain in the plane’. If not fixed, it soaks into the insulation material and can saturate it, and even corrode electrical systems. It also causes the weight of the aircraft to rise, with subsequent increased fuel use. By the time it’s discovered, it can be a lengthy repair.
Slow cabin decompression occurs as a result of an almost imperceptible decrease in cabin pressure. This can be caused by a faulty door seal, which is a very common fault, a crack in one of the windows or a pressurisation system breakdown.
Contamination of the fuel system or malfunction of a component within it, issues with the air conditioning or engine fan blades, worn catches or door locks, instrument failures such as faulty sensors, and general wear and tear all contribute to the minutes ticking away as an aircraft is taken out of circulation. Minor part replacements and defective sensors can usually be fixed within a couple of hours. Issues which require extensive investigative work, or a specific component which isn’t immediately available and has to be flown in from another location, are the AOG situations which every airline wants to avoid.
Getting aircraft back up in the air as quickly as possible creates a great deal of pressure; having a reliable, worldwide, around the clock component supply and repair service is critical to ensuring that issues are resolved rapidly and that the economic and reputational complications of an AOG are minimised.
Aircraft safety is the most vital consideration for anyone involved in the aerospace industry, and passengers embarking on a flight, whether domestic or long-haul, can be reassured that when a mechanical fault develops, the most creative minds in the business will be working on it full time until the plane is completely safe to fly.