Airbus Industrie is working to develop a solution to the recurring problem of engine cowl doors being left unlatched after being criticised by UK investigators following the latest incident on an Airtours A320 that badly damaged the aircraft.
But the manufacturer is reluctant to go along with a formal UK Air Accidents Investigation Branch (AAIB) recommendation that it should implement a cockpit warning of the condition, preferring to focus on the locking system itself.
The UK team says that the Airtours incident, which also led to another aircraft being grounded by debris damage, was at least the eighth since 1992 to an Airbus narrow-body, primarily on International Aero Engines (IAE) V2500-powered machines.
Following the 20 January incident, in which an Airtours V2500-powered A320-200 shed its number one engine cowl doors on departure from London Gatwick and forced it to diver to Stansted, the AAIB is recommending the implementation of flight-deck warning systems to alert pilots if doors are not latched. It notes that warnings are already given if other panels are left unsecured.
Improving the conspicuity of unfastened latches and the training of maintenance personnel "are unlikely to be fully effective", say the investigators, and modification is required to provide "obvious indication" of unlatched doors.
The Airtours incident not only damaged the A320's engine, port wing, control surfaces, fuselage and fin, but cowl debris was also thrown into the main starboard landing gear of an arriving A330-200. That was not found until the aircraft landed in Dubai, where the A330 was rendered unserviceable owing to damage to its gear and starboard flaps.
Two months later the cowl door of an A330-200 fell off during take-off from Vancouver, hitting the wing, fuselage and horizontal stabiliser.
But while Airbus Industrie says it is considering the option of a cockpit warning system, the manufacturer suggests that a task force established to examine the problem appears to be leaning in the direction of a different solution.
An Airbus spokesman says: "Alarms are the first, logical solution, and we are considering this as an option. But we'd have to look at the extra weight, the extra cost, and the extra work for the pilot. We're not sure that the addition of another indicator in the cockpit would be best.
"I don't think an alarm is the favourite idea; the group is more orientated towards looking at the locking system."
IAE has issued several service bulletins as a result of the incidents. Measures outlined to reduce the risk have included painting door latches with fluorescent orange paint, and weighting the latches so that they hang conspicuously when not secured - but none have been mandated.
Airbus says the task force is examining a mechanical solution to remove the ambiguity created when a cowl door is shut. The spokesman says: "Aerodynamics require a smooth surface, so when you close the panels, you will not immediately see that it's not locked. So you can't play on the visual side of things.
"One option is to put in additional parts, so that if the cowl door looks closed, then it is closed. A simple solution is usually the best."
IAE issued a service bulletin last December which suggested modifying fan cowls with an optional "hold-open" device, designed to block full closure of the doors until the device was manually removed.
But few effective measures such as this one have been drawn up, says the AAIB, despite the "appreciable number" of previous cowl loss cases.
And, referring to the Airtours A320 incident, it adds: "Lack of a flight deck system to warn of unlatched fan cowl doors did not appear reasonable, given that such systems were provided for many other access panels on this aircraft type and others in its class."
It is recommending that Airbus should look at incorporating such a system, and that both the European Joint Aviation Authorities and the US FAA consider including a cockpit warning system among future aircraft certification requirements.
Airbus says it has been working closely with engine manufacturers and other parties - particularly over the last two or three years - to address the problem, and says a solution is likely to be implemented "very rapidly, maybe before the end of the year".
However, the manufacturer says that "we are light-years away from mandating any change" to the present regulations, and adds: "It's up to the operators. If they're reluctant to change, if they say this kind of thing won't happen to them because their procedures are well-designed, then what can you do?"
The spokesman says that the problem is largely a man-machine issue, and that a technical answer may not prove to be the best way forward.
He concludes: "This problem is not unique. It's one of several man-machine interface issues that confront us. If a mechanic leaves a spanner inside the engine, how do you fight that?"