Installations and System Design - Line Maintenance

Required Periodic Inspections

It's easy to lose sight of the reasons why some systems in your aircraft must be inspected on a regular basis. For the safety of the flying public (not to mention those of us in aviation for a living), the regulations have identified some key items requiring regular maintenance:

• If the aircraft is flying inside Block B airspace or under IFR rules, then the Altimeter must be accurate within a known level of certainty, and altimetry data transmitted to ground control must be accurate within known limits. For this to happen, the Altimeter and Altitude Encoder must receive accurate static pressure and, together with the Transponder, everything must be functioning well. To ensure this happens, mandatory inspections must be performed at least biennially (i.e. every two years) to test the components in the system, and the integrity of the system itself.
• Unless there are acceptable procedures to avoid it, annual maintenance is required for the Magnetic Standby Compass. Common sense tells us that magnetic directional information must be reliable and accurate and for that reason we must 'swing' the Compass annually and record any errors found on a dated correction card. It stands to reason that any work performed on the aircraft which may affect Compass accuracy will also prompt such a check, or if your compass has a bubble inside, it must be dealt with immediately (compasses that are bone dry with the card spinning around freely are useless).
• Then next most common item for annual inspection is the Emergency Locator Transmitter (ELT). These must be checked for battery condition and proper operation. The installation in the aircraft is just as important and always ensure the portable antenna is not missing. We still encounter some of the early Narco ELT-10's which require a special insulator be inserted in the portable antenna when the fixed antenna is being used. Without this insulator transmission can be too weak to be any use.

It has been our experience that such inspections reveal things such as split, cracked or otherwise leaking static lines, ineffective or damaged moisture drains, sticking or inaccurate altimeters and encoders, and frequently weak transponder output; faults which may not otherwise be detected. Without getting into the reasons for such anomalies, it should be recognized that periodic maintenance really is worthwhile.

Of course there is always more, and, for Canadians, a useful table is given in CAR Airworthiness Manual 571.10 Para. 4 which identifies a lot of the trouble spots and the inspections required to ensure things keep working well.

If you share our concern that aircraft should perform as they were originally intended or have any questions on periodic testing and inspection, please let our experienced staff of specialists help you.