The foundation of conducting an effective External Check is knowing the aircraft. Damage from a previous flight that is missed during an External Check can be attributed to the new crew who either conducted the External Check poorly or caused it! Knowledge, attention to detail and vigilance will prevent things being missed. As well as checking technical items, crews must keep an eye on the big picture on the ramp and be alert to suspicious people or packages.
It is important that flight crew conducting an External Check know:
- what all the visible probes, vents, ports and indicators such as fire bottle discharge indicators are for and what they look like normally. That will make it easier to spot any abnormality.
- what the landing gear locks and steering pins look like and where they are located when fitted. Hydraulic leaks and problems with gear legs can be difficult to spot, particularly by night.
- what the brake wear indicators should look like, if fitted, and when they indicate the need for a brake change. Tyre condition can often seem poor yet be within tolerances. If in doubt get a second opinion.
- which gear doors should be closed and which open. The landing gear bays have been used by stowaways and may even contain a deceased stowaway hidden from a previous flight.
- the potential hidding places for foreign objects – whether equipment, human or a potential Improvised Explosive Device (IED).
- what the flying controls will look like with the hydraulics un pressurised to help identify anything abnormal.
- In modern aircraft made from composite materials damage to the fuselage from vehicle contact can be hard to spot yet from incident history such minor impacts can have a severe effect on the integrity of the structure when it is pressurised.
- how the engine(s) and cowlings are secured, correct reverser stowage and how to spot other things that may indicate damage or previous abnormal engine performance.
- The prescribed content of the external check will be detailed in the Aircraft Operator’s Operations Manual in the form of an expanded check list, and the remarks which follow are generic in nature, highly selective and in no particular order of significance. External checks which are carried out during the hours of darkness require that a torch of effective brightness be carried and used; apron lighting alone is not sufficient.
- Checking tyre inflation visually, especially on multi wheel axles, is difficult if not impossible
- Damage or localised wear can be concealed by ground contact or by restricted visibility of inner tyre walls on multi wheel assemblies. Tyre condition can often seem poor yet be within tolerances. If in doubt get a second opinion.
- Dependent upon the level of confidence in ground service provision, it may be advisable to check that access points are correctly set following the uplift of fluids and toilet servicing.
- Aircraft returning to service following maintenance should be checked with particular care, not only in conducting the normal external checks but also in giving particular attention to those panels that were disturbed during maintenance and their associated fastenings.
- During turn round external checks after longer flights mainly above the freezing level, a specific check for the possible presence of clear ice on the underside of wing surfaces is appropriate even if the ambient ground temperature is above freezing.
- The fitting of covers, flight control locks and landing gear pins should have been recorded in the Aircraft Technical Log, but these items should be checked in case an unrecorded action has taken place.
- If propeller restraints are left fitted after a pre flight external inspection, there should be a formal procedure in place to ensure that are removed before any attempt is made to start engines.