nuts & bolts
maintenance & restoration
Post-Maintenance Inspections Rigorous approach to verifying the airplane’s airworthiness pays off Jeff Simon
recently had my plane painted, ply with a service bulletin. The ture the airplane was level at 2,000 and as part of the painting pro- NTSB report included the follow- feet mean sea level (MSL) for apcess, all of the control surfaces ing: proximately one minute; the pilot were removed and reinstalled. In “The pilot confirmed with the noticed that the airplane began addition, the prop had been re- service center personnel that the ‘pulling’ to the left, and the left aimoved, and almost every mechan- maintenance on the airplane was leron was separated at one hinge ical part of the aircraft had been completed and then proceeded to attach point. The pilot then flew manipulated in some way. preflight the airplane. After depar- the airplane toward an unpopuWhen it was time to pick up the plane and Proper aircraft painting requires a great deal of disassembly. A proper fly it home, the ques- post-maintenance inspection and test flight is critical. tion arose: “Is this aircraft really ready to fly again?” It’s a good question because a significant number of accidents documented in the National Transportation Safety Board (NTSB) reports occur on the first flight following major maintenance. A Cirrus accident involved the improper reinstallation of an aileron following maintenance to com104
This comprehensive and disciplined approach to post-maintenance testing may seem like overkill. However, the NTSB reports don’t lie. lated area, shut down the engine, and deployed the aircraft’s ballistic parachute system.” The first flight of an aircraft following any maintenance should be considered a test flight. Even the most routine maintenance, such as an oil change, can introduce problems that affect the safety of the aircraft. For example, removing an oil filter requires navigating wrenches around mags, harnesses, lines, and wires. It’s not uncommon to find damaged magneto P-leads following oil changes. To make your first flight as safe as possible, you need to have a plan:
Review the Work Completed Your first step should be to clearly identify all work that was completed on the aircraft. This is easy if you were the one doing the work, but it can be more difficult if someone else completed it. If so, it is important to speak to the individual who completed the work, so that you get the complete list. Many good mechanics will take care of small items that are not part of the main job as they come across them. For example, while installing new magnetos, your mechanic may replace some
loose or defective safety wire that he or she spots somewhere else in the engine compartment. Often, these small items never get communicated to the owner.
Assess the Affected Systems Knowing what work was done is important, but it is just as important to learn what other areas were affected by the job. For example, let’s say that you just had your vacuum pump replaced. The pump installation is the obvious place to inspect, but there are also many other affected areas. Was one of the magnetos removed to facilitate the installation? What about the vacuum filters? If they were replaced, that may have entailed work behind the panel. In a twin-engine aircraft, it may have included work in one of the wing
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maintenance & restoration access points to adjust the regulator. Even a simple job can have implications in many other areas of the aircraft. With the space constraints found in many GA aircraft, a technician often has to disassemble unrelated components to get to the job at hand. Once a system has been touched, it needs to be thoroughly inspected and tested.
After a complete and thorough preflight inspection, conduct a ground-run checklist such as one used by mechanics prior to and following annual inspections. When you review the completed work, go through each of the major aircraft systems to see if they were affected. Key systems include flight controls, electrical systems, avionics and instruments,
fuel systems, powerplants, hydraulics, vacuum systems, and landing gear.
Conduct Your Own Inspection Once you have identified everything that has been disturbed during the recent maintenance, carefully examine each system. Look for loose wires, missing screws or nuts, safety wiring, and general security of all components. The best maintenance facilities always have a second pair of eyes look over completed work before closing things up and returning an aircraft to service. If you do your own work, have a friend look things over once you’re done. We’re all human, and no matter how careful we are, it’s our nature to occasionally miss an item.
Develop a Test Plan Let’s be clear; the first flight of any aircraft after maintenance is a test flight. In the military, every aircraft coming out of maintenance must be flown by a test pilot and thoroughly checked out using a detailed test card. There is no reason for you to do anything different. Develop a “standard test plan” and add to it as needed to account for the work recently completed. After a complete and thorough preflight inspection, conduct a ground-run checklist such as one used by mechanics prior to and following annual inspections. These ground tests include the following items: Q Warm up engine Q Run-up magneto check Q Carb heat check QBrake check 106
Following up on your test flight is important as well. After you complete your test flight, return to the airport, shut the aircraft down, and begin your post-flight checks. Q Full throttle static rpm check Q Propeller and governor check Q Ammeter/vacuum/fuel pressure/oil pressure (idle and full power) Q Idle check Q Mixture cutoff check Q Ground check of avionics Q Control systems check All of these checks should be compared with a pre-maintenance test so that you have a baseline to compare to. Your test flight plan should be controlled. A typical post-maintenance test flight plan might include the following: Q Fuel and load aircraft well below max gross weight Q Taxi into position and apply full brakes Q Engine run-up to full throttle static rpm Q Brake release Q Rotate at V X , climb at V Y straight to 1,000 feet AGL Q Begin climbing turn, circling within 1 nm of the airport until reaching 3,500 feet AGL Q Level aircraft and continue climb to 4,500 feet AGL, maneuvering as necessar y to remain within 5 nm of the airport Q Test operation of all flight controls Q Test operation of all engine controls Q Test operation of propeller EAA Sport Aviation
Q Test operation of landing gear (within speed restrictions) QTest avionics as required
Fly the Plan and Follow Up Just as the first post-maintenance flight becomes a test flight, you become a test pilot. It’s important that your piloting skills are up to the test. How recently have you
performed a simulated engine-out landing? Do you know where your emergency landing sites are if you cannot make it back to the airport? If your aircraft has been out of service for a long time, you should consider getting yourself current in another plane before becoming the test pilot on your aircraft. Never carry a passenger on a test flight. The added distractions and
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maintenance & restoration unnecessary risks to your passengers are a recipe for disaster. The sole exception is when your flight test includes significant avionics testing. If this is the case, two test pilots are required: one pilot to fly the aircraft and another pilot to run the avionics testing. Your first post-maintenance test flight is no time to have your head stuck
down in the cockpit testing and/or monitoring gauges and avionics. Following up on your test flight is important as well. After you complete your test flight, return to the airport, shut the aircraft down, and begin your post-flight checks. The flight test may seem successful from the cockpit, but not so in the engine compartment. Do a thorough post-flight inspection
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to check for fluid leaks, flight control security, and other potential problems. If you find a problem, fix it and run the complete test over again. Even if no problems showed up during the flight test, you should still hold off from flying crosscountry, over water, or in IFR conditions until you have a few more
Even if no problems showed up during the flight test, you should still hold off from flying cross-country, over water, or in IFR conditions until you have a few more flights logged,
just to ensure that no gremlins are lurking
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around. flights logged, just to ensure that no gremlins are lurking around. To many people, this comprehensive and disciplined approach to post-maintenance testing may seem like overkill. However, the NTSB reports don’t lie. First flights after maintenance are not something to take lightly. For my part, I’ll be doing some really thorough inspecting before I take my newly painted beauty back into the air where she belongs. Jeff Simon is the president of Approach Aviation (www.approachaviation.com), a provider of educational products, tools, and supplies for aircraft owners. 108