If you inquire with an experienced aviation mechanic about which flight poses the greatest risks for an aircraft, you might be taken aback to learn that it is the initial flight following significant maintenance, such as an annual inspection. This insight came to me during my time at a flight school, where the Certified Flight Instructors (CFIs) performed the “return to service test flights.”
This is in accordance with FAR 91.407, which stipulates that “[if] the aircraft has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight, it cannot be released for rental until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, performs an operational check of the maintenance or alteration made, and logs the flight in the aircraft records.”
The chief mechanic would provide a checklist of items to inspect or verify before you took off. These post-maintenance flights were typically conducted in the morning prior to the school opening, with CFIs taking turns. If you were rated to fly that aircraft, it was an excellent opportunity to gain some currency or proficiency.
Initially, I questioned whether the mechanics were merely joking about the risks associated with the post-maintenance flights. However, my review of National Transportation Safety Board (NTSB) accident reports confirmed their warnings. Numerous incidents occurred during the first post-maintenance flight that ended poorly, highlighting why mechanics emphasize the need for caution.
Takeaway: If a mechanic advises you to ground the airplane or indicates a no-go, heed their advice.
This lesson was underscored one April day when I witnessed a newly serviced Beech Bonanza experience engine failure shortly after takeoff, landing in a field beyond Runway 34. I was on the ramp conducting a preflight inspection of a Cessna 172 when the engine quit, followed by a shout from the airport restaurant deck. When I glanced over, I noticed several individuals standing and gazing toward the north.
The pilot in command was the aircraft owner. He landed the plane safely in an undeveloped field adjacent to the airport, escaping without injury and sustaining only minimal damage—a collapsed nosewheel. He could have ended up on the busy road separating the airport from the field, or in the nearby neighborhood, or even in the shopping center parking lot situated on the extended centerline of the runway.
The off-airport landing stemmed from an uncommanded loss of engine power during that first post-maintenance flight.
A mechanic involved with the aircraft—and corroborated by the NTSB report—indicated that the aircraft had just exited maintenance. The owner had completed a run-up and noted the uncommanded loss of engine power. The report stated that the “airplane was towed back to the maintenance shop, and a mechanic recommended that the pilot await a thorough examination.”
The shop was busy with other projects that day, and they couldn’t allocate time for diagnosing the Bonanza. The search for the cause of an unexpected engine power loss is a task that should not be rushed.
The NTSB reported that the pilot had approximately 300 hours of total flight time, with 120 hours logged in the accident aircraft. He downloaded the engine data from the aircraft’s monitoring system to analyze at home. Upon returning to the airport later that day, he informed the mechanic that he had observed no anomalies in the data and boarded the airplane for the ill-fated flight.
One mechanic remarked that the flight occurred AMA (against mechanic’s advice). As the aircraft climbed to about 350 feet, it lost engine power without warning. There were no unusual sounds—just an unsettling silence.
The post-accident inspection of the engine revealed that the B-nut to the fuel pump inlet was loose. The probable cause identified by the NTSB was a “total loss of engine power due to fuel starvation as a result of a mechanic’s failure to properly tighten the B-nut during a recent annual inspection. Contributing factors included the pilot’s decision to take off despite signs that the engine was not functioning normally.”
3 Key Considerations
Over the years, I have heeded mechanics’ advice and compiled a list of critical points to be vigilant about during the first post-maintenance flight:
Cross-rigged controls: The first flight following annual maintenance requires a thorough and methodical preflight inspection. With checklist in hand, carefully examine the airframe to ensure everything is in order. Pay special attention to ensure that “flight controls are free and correct.”
Do not allow distractions to interfere during this inspection. If interrupted, restart the process from the beginning. I know of two accidents that resulted from incorrect control rigging, one of which was fatal. I also firmly advocate for performing a “full military box” during the engine run-up to confirm full and correct control movement.
Seats and seat rails: It’s vital to double-check that the front seats are properly installed and secured, particularly in a Cessna 100 series. Ensure that the pins from the bottom of the seat are fully engaged in the seat-rail holes.
The seat rails should have stops that secure the front and rear sections of the rail to prevent the seat from slipping off. Over time, wear can elongate the pin holes, rendering them ineffective. The so-called “seat rail AD” was enacted after a fatal incident where a pilot’s seat slid backward during takeoff.
Engine compartment: Take extra time to inspect the engine compartment with a flashlight, looking for any foreign objects. One of my mentors, who instructed aircraft carrier pilots during the Vietnam War, recounted a harrowing tale of a squadron member who had to eject when his Douglas A-4 Skyhawk lost engine power due to a rag left inside.
The typical protocol for test flights involves making several passes over the airport to verify engine reliability—just to keep safety in check. Don’t be surprised if the mechanic is awaiting your return from the flight.
Most mechanics take great pride in their work and recognize that their job isn’t complete until all paperwork is finalized, logbook entries are submitted, and the test flight is executed.
Based on an article from flyingmag.com: https://www.flyingmag.com/first-postmaintenance-flight-should-be-treated-with-caution-and-respect/
