FAR's 91.411 and 91.413

by Marco
(Switzerland)

1. If a customer operating an Airbus A-320 is requested to comply with FAR 91-411 and FAR 91-413, is it necessary to test only the STBY altimeter system or also the main systems?

ANSWER:

Note: FAR Part 91.411 and 413 are operational rules and only apply to aircraft operated within controlled U.S. airspace under instrument flight rules. So if the A320 is operated outside the U.S., the applicable national authority rules would apply.

FAR 91.411

The main altimeters in the Airbus A320 are considered air data computer types that incorporate air data corrections internally (FAR 43 Appendix E (b)(2)), so they may be tested in accordance with the manufacturer's test specifications. At what frequency is the question. The literal interpretation of the rule would require that the inspection to be performed (using mfg. test specs) every 24 months. However, it has been argued that if you follow the periodic tests required by the manufacturer of the air data computer system (not Airbus), that would meet the requirements of the rule. What does the manufacturer recommend? If they have no recommended interval for inspection and test, I would say the interval required by the regulation would apply.

Standby altimeters fall under FAR 43 Appendix E (b)(1). This is pretty strait forward and these must be removed and sent to the shop where they can be artificially run up to altitude to test the variation (if any) from the specifications listed in the appendix. This must be done at 24 month intervals.

Every 24 months (to meet the requirements of FAR 43 Appendix E) you must also determine through tests and inspections the integrity of the static system and skin condition around the static ports.

2. Isn't it enough to follow the various AMM tests available for STATIC systems and ATC?

ANSWER:

Both FAR 91.411 and 413 state that the inspections must be performed in accordance with FAR 43 Appendix E and F. If the AMM follows this criteria exactly, then yes.

3. The ATC/Mode S must also include an altitude reporting check on several simulated altitudes with Pitot/Static test-set?

ANSWER:

FAR 91.413

Yes, an integrated system check for ATC/Mode S transponders must also be performed every 24 months. The inspection required by FAR 91.413 can be done on the bench or on the aircraft as long as all the tests outlined in FAR 43 Appendix F are performed.

The integrated system test could be required sooner then 24 months if there is a removal/installation or maintenance on the automatic pressure altitude reporting system of the ATC transponder where data correspondence error could be introduced. This is stated in both FAR 91.411 and 91.413.