Which aircraft maintenance repairs require a test flight?

Question

14 CFR 91.407 requires an "Operational Check Flight" of an aircraft before passengers may be carried in certain situations:

§91.407   Operation after maintenance, preventive maintenance, rebuilding, or alteration.

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(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.

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Does the FAA have any guidance that includes examples which better explain the bolded section from the regulation? It seems like that could be open to interpretation which could lead to different people having different ideas about when an operational check is required.

For example, is one required for routine maintenance like an engine change or prop change? What about a flight control change or a flap change? A new paint job (including the flight controls)?

Answer 1

I've been in aircraft maintenance for over 15 years, and have worked about 10 different types of narrow and wide body aircraft, and have never once seen a maintenance manual direct me to test fly an aircraft.

There is a reason for this, though. Repairs done during routine maintenance are designed by the manufacturer such that the repair itself makes the aircraft airworthy. That is usually part of the manufacturing and STC process, if I'm not mistaken.

That being said, it's not entirely uncommon to have maintenance control or even maintenance management request a test flight. Usually this is done for troubleshooting or for repair verification. This is largely due to the fact that there are some problems that maintenance cannot duplicate on the ground. For example, I recently worked an airplane whose window heat failed at the top of descent about once every ten or eleven flights. I can simulate a lot of things on the ground, but what I can't simulate is the actual descent of the aircraft at about 37,000 feet! The problem had been ongoing for four or five months, but was sporadic enough not to trigger any alarms in the analysts office. It was only when you paid careful attention to the history of the problem that you realized it had major issues.

Due to regulatory requirements, and the way our GMM is written, if the aircraft had another occurrence on the next flight, it'd be "dead" at the next station it landed with no MEL relief. We made a repair, but it was really only a guess because there were no actual signs of wear/fatigue/damage and everything tested normally. Management requested a test flight, and asked the test crew to run it through the wringer, to see if it would fail.

On the other hand, there are certain systems that may require flight crew verification during flight prior to recertification. An auto land system that has had chronic failures may require the flight crew to perform an automatic landing before it can be recertified back to full CAT III landing status. But, this can often be done on a revenue flight, and is often not a dedicated flight meant to specifically test the system.

There is also the rare case in which major structural repairs may require a test flight. I once saw a wide body aircraft that had a tail strike on landing. The damage was so severe, it literally twisted part of the empennage. In order to be repaired, our company required major involvement from the aircraft manufacturer. The manufacturer did provide a repair, but for obvious reasons, the engineers actually mandated several test flights afterward.

However, as far as I know, there is no regulatory requirement which says that a certain repair requires a test flight. From what I've seen, and perhaps this may sound awful, you kind of "know" when an airplane needs a test flight.

Answer 2

I found this on a website about STC Certificates and aircraft modifications:

a. Applicant Flight testing precedes issuance of the TIA. The FAA will >review the applicants flight test reports and repeat some or all of the >tests as necessary. These repeated tests will be identified and performed >per the FAA issued TIA.

b. FAA will perform flight tests for modifications which could affect the >aircraft's performance, flight characteristics, powerplant operation, >and/or overall handling qualities. Changes to systems, equipment, >instrumentation, and flight manuals may also require flight tests. Any >modification which may affect the noise signature and/or navigation of the >aircraft (including performance changes) will usually require fight >testing. The FAA project engineer can provide general information on the >types of tests which may be required.

NOTE: Successful completion of the TIA tests by the FAA is one of the final >steps to STC issuance.

c. Applicant testing.

(1) Research and development flight tests are to ensure the design changes >are in compliance with the applicable 14 CFR's. The FAA will not >participate in or witness these tests. However, the FAA will discuss and >provide general guidance in order that such tests can be made meaningful >and safe. Alternatively, a Flight Test Pilot DER may be utilized to perform >such tests.

(2) Flight test proposals are based on the knowledge of the modification >and development tests. The proposal should be based on the certification basis and include recommended tests, instrumentation to be used, necessary safety equipment, data acquisition, and reduction methods. Upon approval of the test proposal, descriptive and compliance data, and conformity established with the data, the FAA will issue a TIA. FAA flight test personnel should then be contacted to assure that potential hazards are recognized, the required test methods and criteria are understood, and for concurrence.

NOTE: An applicant's flight test report should be submitted to the FAA for review upon successful completion of the inspection and test requirements equivalent to those required in the TIA.

d. FAA testing may include repeating of tests, partially or in their entirety, to verify compliance to the certification requirements. FAA testing may be accomplished by an FAA pilot or an authorized DER flight test pilot.

e. Installation Conformity inspection of the modified aircraft to be used for flight tests will be performed by the FAA or FAA designee prior to FAA testing. If discrepancies are found, they should be corrected and any test which could have been influenced may be repeated before further tests are performed by the FAA.

f. Aircraft weight and the Center of Gravity (CG) location that is current and accurate is extremely important to assure the modified aircraft can be loaded to the critical weight and CG limits for flight testing. The aircraft to be used for official flight tests should be weighed and witnessed by an FAA representative before testing begins. The resulting weight and balance determination will be carefully checked by the FAA and, when found to be accurate, will be used for all subsequent flight test weight and CG calculations.

g. Ballast necessary for flight testing should be securely restrained in such a manner as to withstand the inertial loads resulting from a survivable emergency landing. The preferred form for ballast is small, solid pieces of a high density metal (lead, cast iron, steel, or depleted uranium) fixed to the structure or in a suitable container that is fixed. Using passengers as ballast is not acceptable.

h. Instrument calibration, when required, should be accomplished by an approved instrument repair inspector prior to the FAA flight test program with calibrated cards provided. Types of instruments to be calibrated may include: altimeters, tachometers, temperature gauges, airspeed indicators, etc. Calibrations should be performed within 3 months of the test. However, on critical items, this requirement may be 30 days.

NOTE: Usually, the entire airspeed system is calibrated before flight testing.

i. Rapid emergency egress provisions will be demonstrated to the FAA inspector and pilot for acceptability prior to FAA flight tests. Parachutes will be provided to the FAA, if required.

j. Experimental Airworthiness Certificates, or special flight permits, are issued before operation for any aircraft which does not have a valid TC, or does not conform to its TC. Although the operations may eventually lead to a TC, they may be conducted only as a matter of research, or to show compliance to the appropriate 14 CFR.

k. Flight manual supplements, or if an FAA approved Aircraft Flight Manual (AFM) does not exist, a supplemental flight manual, if required, will be provided to the pilot as a result of the modification, regardless of the method used on the original aircraft. A draft flight manual should be provided to the FAA prior to any flight tests. After FAA flight testing, the draft manual should be finalized and submitted for FAA review and approval. A guide for the format and preparing of a supplemental flight manual is provided in appendix 5 of AC 23-8A, AC 27-1, and AC 29-28.

NOTE: The aircraft TCDS should be checked for identification of the FAA approved Aircraft Flight Manual, if appropriate. TCDS of many older aircraft state placards and markings are required (in lieu of a flight manual). Manufacturer owners' manuals may not be FAA approved.

Here is the link to the page: http://www.astech-engineering.com/systems/avionics/aircraft/faastcprocess8.html