Does current latch design continue to account for inspectability & maintainability? Is a new and safer approach needed to secure engine cowlings?
By Rus Sutaria – Avia Intelligence Ltd.
The recent incident involving British Airways adds another installment to that which is the occasional drama of disappearing engine cowlings on Airbus A320’s. There appear to be parallels with the JetBlue incident, and it is without reasonable doubt, that the debate regarding latching mechanisms will invoke the usual finger-pointing regarding design issues, not least an apparent inadequacy in terms of maintenance and operational practice.
A British Airways Airbus A320 suffered the total loss of cowlings for both No.1 and No. 2 engines (together with an apparent engine fire) whilst departing from London Heathrow Airport for Oslo on Friday May 24, 2013. The pilots immediately turned the aircraft back to the airport, where an emergency landing was expertly executed at 08:43 BST. The accident investigation is on-going, with a view to determining the probable cause of the incident.
This and previous incidents involving engine cowling latches, appear to have highlighted a potential human factors weakness, not only in terms of design, but also in terms of inspectability and maintainability. There are distinct differences to the design and functional approaches where correct engine cowl security is concerned, and an even wider variety of SOPs for both pilots and maintenance engineers to follow in the pursuit of safely secured engine cowlings.
It is interesting to note, that all of these instances occurred during either the take-off or climb-out phases of flight (most notable JetBlue A320 in 2010), and were the result of unlatched or incorrectly latched engine cowls, following complex tasks like borescope inspections and maintenance of the IDG.
Although duplication inspections exist where engine maintenance is concerned, the circumstances of when engine duplication inspection is required, is perhaps not as clear as it should be. From the maintenance human factors perspective, it would not be surprising if the confusion surrounding duplication inspection, may be one of the causes of a potential failing that seems to crop-up not only on A320s but also on other aircraft types as well.
Pilots have become increasingly wary of this issue, and indeed captains direct their first officers to pay particular attention to ensuring engine cowlings are securely closed and locked. Some captains have even been reported going as far as to instruct close inspection by kneeling-down and taking a proper look at the latches. In all truth however, you really would have to be on your knees to be able have a clear view of the latches on some of the aircraft. Let’s face it, which of us would want to do that on a wet ramp!
The problem here is two-fold, and revolves around redesign of latching mechanisms and the far more prevalent issue of inspectability of the same. Designing a foolproof system that completely eliminates the risk of incorrect or absent latching of engine cowlings is an unreasonable proposition. Any solutions will need to make an incorrectly secured or completely unsecure engine cowling far easier to spot by both maintenance personnel and pilots alike.
Previous experience suggests that there are other means by which these occurrences can be made apparent. An open cowling on the No. 3 engine of a B747-200B had been identified as a result of the flight-deck crew observing excessive vibration following the engine-start. A loose or insecure engine cowl has the tendency of magnifying natural engine vibrations, something that engine instrumentation should easily pick-up. In this instance, an alert flight-deck crew questioned the anomalous readings and decided to taxi the aircraft back onto stand so that an engineer could investigate and resolve the matter.
Ultimately an ounce of prevention is always better than a pound of cure. Hence a combination of improved inspectability through design and maintenance practices might just do the trick (Not least, closer attention to detail during the pilots’ walk-round). It may also be a simple matter of equipping our engineers and even pilots with a simple tool like an inspection mirror, thus facilitating a better view of the underside of the engine and its associated latches.
On the other end of the spectrum a complex and undoubtedly more costly solution may be necessary in the form of ECAM or EICAS display messages that highlight unsecured or incorrectly secured engine cowls, in much the same way as open passenger and emergency exit doors would be indicated.
There can be no real conclusion to this problem short of better design, operational and maintenance practice. The most worrying part of all this is the shortening odds with regard to a potential fatality. If safety is the prevention of that which we do not want to happen, then we need to stop tinkering with this problem, and start resolving it!