If you ask a seasoned aviation mechanic what flight is the most risk-prone for an aircraft, you may be surprised to hear that it’s the first flight after significant maintenance, such as the annual inspection. I learned this when I worked at a flight school that had the CFIs do the “return to service test flights.”
This follows FAR 91.407 (b), which states “[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 and makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.”
The chief mechanic would give you a list of things to check and/or verify when he sent you on your way. These post-maintenance flights were done in the morning before the school opened, and CFIs performed them on a rotating basis. As long as you were rated for that aircraft, it was a good way to get some currency or proficiency time.
At first I wondered if the mechanics were just joking with me about the risk involved in the post-maintenance flight, but a review of National Transportation Safety Board (NTSB) accident reports backed up their admonishments. You’ll find many instances where something happened during the first post-maintenance flight that went badly—so, it’s no wonder mechanics urge caution.
Teachable moment: If the mechanic grounds the airplane or tells you no-go, listen to them.
This was hammered home one day in April when I witnessed a fresh out of maintenance Beech Bonanza lose engine power shortly after takeoff and end up in a field off the end of Runway 34. I was on the ramp doing a preflight inspection of a Cessna 172 when I heard the engine quit, followed by a loud exclamation coming from the deck of the airport restaurant. I looked over to see several people standing up and looking to the north.
The pilot was the owner of the airplane. He put the aircraft down in an undeveloped field across the street from the airport. He wasn’t injured,t and the airplane damage was limited to a collapsed nosewheel. The pilot could have come down on the busy four-lane road between the airport or in the neighborhood just to the east of the field or in the parking lot of the shopping center off the extended centerline of the runway.
The off-airport landing was caused by an uncommanded loss of engine power during the first post-maintenance flight.
According to a mechanic who worked on the aircraft—and according to the NTSB report—the day of the accident the aircraft had just come out of maintenance. The pilot/owner had performed a run-up and noted an uncommanded loss of engine power. The report said the “airplane was towed back to the maintenance shop, and a mechanic recommended that the pilot wait until a more detailed examination could be completed.”
The mechanics said the shop was busy, and they were hip deep in a project and couldn’t break away to diagnose the Bonanza. The search for the cause of an uncommanded loss of engine power is not something you want to rush.
According to the NTSB, the pilot, who had a little under 300 hours total time, of which 120 were in the accident aircraft,”downloaded the data from the airplane’s engine data monitor and took it home to examine. After returning to the airport later that day, the pilot reported to the mechanic that he did not observe anything abnormal in the data, and he got back in the airplane to depart for the accident flight.”
One mechanic told me the flight was AMA (against mechanic’s advice). The aircraft was approximately 350 feet above ground during the climbout when the engine lost power. There were no abnormal noises or sounds—just the loudest quiet a pilot can experience.
The postcrash inspection of the engine revealed that the B-nut to the fuel pump inlet was loose. The NTSB’s probable cause was listed as a “total loss of engine power due to fuel starvation as a result of a mechanic’s failure to properly tighten the B-nut to the fuel pump inlet during a recent annual inspection. Contributing to the accident was the pilot’s decision to take off despite indications that the engine was not operating normally.”
3 Things to Watch For
Over the years I’ve listened to the advice of mechanics and have a list of things to be extra cautious about during that first post-maintenance flight:
Cross-rigged controls: The first flight after annual begins with a very careful and methodical preflight inspection. Checklist in hand, go over the airframe like there are pieces of gold hidden on it. Be particularly careful about the “flight controls free and correct.”
Don’t let anyone or anything distract you during this. If you are interrupted, start over from the beginning. I know of two accidents caused by improper control rigging—one of them was fatal. I am also a big fan of the “full military box” during the engine run-up to verify correct and full control travel.
Seats and seat rails: Double-check that the front seats are in and locked, especially if you are on a 100 series Cessna. The pins from the bottom of the seat should be fully seated in the seat-rail holes.
Also, the seat rail should have stops attached—they are basically a piece of metal securing the forward and aft part of the rail. These keep the seat from sliding off the rail.
Over time, the pin insertion holes can elongate, rending them unusable. The so-called “seat rail AD” came about after a fatal accident attributed to a pilot’s seat sliding all the way back during takeoff.
Engine compartment: Spend extra time with a flashlight looking for anything that doesn’t belong there. One of my mentors, an instructor for aircraft carrier pilots in the U.S. Navy during Vietnam, told a chilling story of one of his squadron members who was forced to punch out when the engine of his Douglas A-4 Skyhawk lost power in flight due to a rag left in the engine.
The protocol for test flights is often to do a few laps over the airport to make sure the engine is reliable—just to be safe. Don’t be surprised if the mechanic is waiting for you when you get back from the flight.
Most mechanics take great pride in their work and know their job is not done until the paper work is done, logbook entries made, and test flight completed.
