AircraftOwner Online

I’m talking about access panels—those nondescript and unassuming little doors that hide the working parts of your airplane. These include the round, oblong, or square access panels that mechanics use to peek, poke, and prod inside an airplane during maintenance. On general aviation airplanes, sheet metal or machine screws typically hold these panels in place. Snap latches, such as the flush Hartwell-type latch, often secure the engine-access panels. On larger aircraft, the panels may be held in place by quick disconnect fasteners or other specialized types of hardware, such as Dzus or camlock fasteners.

A Proper Preflight…

What’s the big deal with access panels? One issue is ensuring their security. Pilots routinely open certain access panels during the preflight inspection to check important systems on the airplane. A typical access panel used by pilots is one designed for checking and servicing engine systems. For example, access panels must be opened in order to check the oil level or drain the gascolator. These panels must also be carefully and completely secured by closing the access door and ensuring the latch mechanism is fully engaged.

One of the many things you should have learned about preflight inspection is how to determine that the latches have engaged. Typically, cues, such as a distinctive clicking sound, tell you that the latch has engaged and is locked. Still, don’t move to the next preflight item until you have double-checked and verified the security of any access panel door that you have opened.

…Prevents Problems during Flight!

If you think that a loose or missing access panel is minor, consider these examples.

-A corporate jet returned to the airport shortly after takeoff with the crew reporting a loud banging noise emanating from the tail area. After landing, an inspection revealed that one of the pilots had not properly secured the forward latch on the fueling panel during preflight. When sufficient airflow got under the half-latched panel door it blew open and began banging in the air stream—creating a loud noise and damage to those parts of the airplane it had “attacked.” It took about $7,000 and a day of down time to get the aircraft back in service.

-An Australian-registered amphibious aircraft lost an access panel on one of the floats during flight. The access panel struck the right horizontal stabilizer, causing considerable damage and leading to control issues. Specifically, the airflow across the open access hole caused vibration of the hydraulic lines, which failed and caused loss of hydraulic fluid. One result was partial loss of the landing gear extension system.

-A single-engine Cessna aircraft returned to the airport after the pilot complained of a “buzzing noise” that started above 60 knots. An inspection revealed an underside horizontal-stabilizer access panel had only one screw holding it. Once the air flow became sufficient, the panel began vibrating against the stabilizer structure, which caused the “buzzing.” A new panel and some touchup paint got the airplane back in airworthy condition. The mechanic had to pay the bill since he had not properly secured the panel after maintenance.

-An accident was barely avoided on a training aircraft after a mechanic opened the access panel on the underside of the wing to perform a check and left it open while briefly returning to the hangar. A student pilot was scheduled to use the airplane for his next training flight. Thankfully, though, he found the open access panel during his preflight inspection and asked why it was open.

Lessons to Learn

Any good preflight must include a thorough inspection of all access panels. Check for loose or missing hardware, condition of the panels, and, most importantly, security of the panel. Make sure that you check the underside of the fuselage, wings, and stabilizers. Address any concern before starting the engine.

A final caution: Never assume that simply securing an open panel will take care of the issue. As in the case of the student pilot described above, you need to find out if any maintenance tasks are incomplete. An open panel may indicate that a mechanic started maintenance on the aircraft. Loss of an access panel may be minor in comparison to taking off in an aircraft with incomplete maintenance tasks.

Barry Ballenger is an aerospace engineer with the FAA Small Airplane Directorate in Kansas City, Missouri. He also holds an A&P with Inspection Authorization and is a private pilot.