THE IMPORTANCE OF SITUATION AWARENESS IN AIRCRAFT MAINTENANCE

While situation awareness is almost synonymous with flight crew, there is not enough mention on that issue with respect to maintenance aspect of aviation. Situation awareness occurs when knowledge of present aircraft configuration marries the intended, as a result of maintenance, be it in phases like inspection, defect rectification, major / minor teardowns, restoration and the extent of system interrogation. Changing aircraft configuration from one phase to another, within the realms of maintenance, does possess numerous dangers if any of the following is left found wanting; communication across all staff directly involved in operational aircraft maintenance, expertise in system as well as sub-system behaviour across different modes - with or without degradation in capabilities, and serviceability of equipment and applicable infrastructure. Elements like complacency, over confident with operating environment as well as lack of familiarity – unaware of potential dangers or even heightened anxiety causing the mind to lose track of issues that may not be priority but critical nonetheless, are all issues that the aircraft engineer has to content with, in a concerted attempt to have reasonable situation awareness at work.

In a recent incident, an ETOPS (Extended Twin engined Operations) rated aircraft was scheduled to perform routine heavy maintenance check at a hangar. The aircraft was already in maintenance phase, having being docked into the berthing premises. Power was cut from the aircraft systems after high lift devices at the trailing edges were fully extended while those at the leading edges were partially extended. In addition to that, the engine cowlings were also fully extended. This configuration was required so as to provide access for inspection, servicing, lubrication and replacement of components. However, there was a need to perform some defueling which was necessary for repair work to be performed. This situation paved for the first sign of trouble. The check package was already decided before aircraft arrived at hangar for maintenance. Defueling requirement, if any, should be made known and available to the operational staff, who will only carry out tasks as per job cards mandated by the customer’s planning and quality departments. Due to lack of consistent and effective communication between lateral and multi-layered management, this requirement was not made known to the ground staff. Since the fuel bowser could not gain entry into the aircraft defueling point by the rear of the wings (docking facilities hindering), there was no other option but to go through the front (wing leading edges). However, the leading edge high lift devices were extended (as mentioned above) and hence had to be retracted to admit fuel bowser entry without obstruction / impact to the vehicle. One engineer positioned himself on the ground to provide clearance instruction to another, who was waiting at the cockpit, in order to operate the flight controls. The operation of both leading and trailing edge is controlled by one lever at the flight deck, for primary mode of control. The power source of operation under this mode is hydraulics. The said lever was at the fully extended detent which, while matching with trailing edge flap configuration, does not match with the leading edge slat configuration. The associated hydraulic power was invoked after necessary clearance was obtained from the ground. Immediately, system was triggered to match flight control lever position to that of actual flight control surfaces position. A loud sound (unnatural one amidst the many heard in daily maintenance) ensued at the same time; emanating from two different points. The leading edges had impacted the inboard cowlings at both wings, causing puncture to the cowlings (as well as the associated load sharing members of the engine) and similar damage to the slats.

On a separate incident, a new four-engined European aircraft was being towed in from apron to the hangar for some unscheduled maintenance. Normally aircraft movement into and out of hangar premises would be conducted by hangar personnel as they are conversant with the terrain as well as the impending dangers of moving within congested spaces. On this instance though, towing operation was conducted by line maintenance personnel, who normally conduct transit and short layovers within the confines of the airport bays itself. As far as towing inside hangar is concerned, it is mandatory to have wing tip watchers at any point in time. However, the technicians delegated for this task were not at the tow vehicle themselves; they had to obtain necessary security clearances in order to be admitted into the hangar premises. On the other hand, the engineer who was towing the aircraft was under pressure from the Apron to evacuate the taxi-way. Once he evacuated, he proceeded to tow further in, as he received information that his colleagues were still stuck to complete security clearance paperwork. Within seconds, there was a loud sound. The most outboard engine at the port side had impacted a tall engine maintenance stand. This stand was placed at a location where no equipment is allowed to be stored, for any reason, by existing Company policies. There were no chevron markings or any form of warning signages advising as such. The resulting damage was assessed to be so extensive that the affected engine cowling was certified beyond economical repair.

Both incidents highlight different aspects of shortfalls in varying degrees and forms. In the first instance, the engineer was wrong to operate the flight controls by invoking hydraulic power; he should have controlled using electric power instead. The control for this secondary mode is not the same as the lever mentioned earlier; it is operable by virtue of an “EXT / RET” rotary selector. If he had utilised that option, the ground engineer who was providing clearance would have been able to foresee the impending impact and stop movement, as necessary. However, there is no such provision if elected power source is hydraulics. This highlights serious need for heightened situation awareness levels of aircraft configuration, with regards to uniformity between circuitry as well as ambient physical conditions. As far as the second incident is concerned, the engineer was unfortunately guilty of operating in a new environment, heightened situational awareness was found wanting. In addition, he could have chosen to explain to Apron service that he can only move further once he has the necessary ground support. By proceeding on, he took a huge gamble. Even in this condition, the resultant damage would not have occurred if there were no obstructions. CCTV footage was studied and it showed evidence that a senior engineer had placed the stand there at the end of scheduled heavy maintenance, a few months ago. The area has seen been vacated and a prominent chevron marking drawn to warn future towers.

While both incidents did not result in any injuries to the human operators, the lessons learnt as a result of extensive damage on both aircraft suggest that situation awareness can never be plateaued; the engineer on the ground is ultimately responsible to marry operational configuration of aircraft with intended goals, while taking into key considerations pertinent elements like legalities, safety and quality concerns.


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Idris


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