Acknowledgements: Thomas P. Turner, (Mastery Flight Training, Inc./Flight Instructor Hall of Fame inductee)

Any engine work carries with it the need for thorough testing. It may be that the shop that does the work completes a full flight test profile before calling you ...... Much more commonly, the engine has probably been run up on the ground but never flown before the owner comes to take it home. Even if the engine shop has flown the airplane, you should still approach flight after engine work sceptically and cautiously. Getting an airplane returned to service after engine repair, modification or replacement is a team effort, and you as pilot-in-command are a vital part of that team.

For a couple of years in the 1990s I was chief pilot for an engine modification firm, test-flying airplanes, then checking out new owners on the modified airplane.

I was what is called a production test pilot. It sounds exciting ... but most of the time it’s a fancy term for flying around in circles within gliding range of an airport while recording lots of engine data to be studied on the ground and applied to making corrections before calling the engine work complete.

 It did get “exciting” once to twice, but not terribly so. That said, you have to be ready for any loss of power, whether partial or total. The most important point is this: you do not want to pay the bill, jump in and fly away without giving the engine a thorough check. If you’ve had anything more than an oil change done on your airplane’s engine, you’re a production test pilot too

 Here is what I did with newly installed or modified engines. You may want to do the same:
Flight 1

  1. Make a very detailed engine compartment inspection with the cowling off. Check all connections and hoses. Determine the reason for any visible fluid — fuel, oil or other — before going further. Clean the fluids and, with the mechanic, ensure there are no active leaks.

  2. After the cowling has been installed, make another detailed inspection of the engine compartment. If you find fluids now there’s a leak that must be addressed before starting the engine.

  3. Assuming all is good so far, start the engine. Confirm temperatures and pressures are as expected while idling the engine. Check electrical system operation, and vacuum or instrument air operation. Run the engine three minutes or so, then shut it down.

  4. Make another detailed visual inspection of the engine compartment, looking especially for any signs of leaks. If there are any leaks, back into the shop it goes.

  5. After passing this engine run leak test, start it up again. Conduct ground operations and an engine run-up in accordance with the break-in instructions the engine manufacturer or your shop provides (even replacing a single cylinder means a break-in process). This usually means minimising time at low power on the ground, but ensure you pay very close attention to engine temperatures and pressures during that time. If anything is abnormal, take the airplane back to the shop and have a mechanic investigate.

  6. Assuming all is normal, make a normal take-off. Ensure correct fuel flow, temperatures and pressures at take-off power. If anything is abnormally low or high, abort the take-off or if in the air immediately return to land to have the condition checked by a mechanic.

  7. (Assuming all is still normal), cruise-climb following the airport traffic pattern. (If airspace permits), climb to two or three times the height of the traffic pattern altitude. This keeps you continuously within gliding distance of the runway should anything require a quick return to land or in the event of serious engine issues.

  8. Fly a rectangle course over the airport for 15-20 minutes. Follow the manufacturer’s or shop’s engine break-in directions.

  9. Land. After shut-down conduct a visual inspection of the engine compartment, looking especially for any signs of leaks, loose or pinched hoses or wires, and/or chafing from vibration and contact.

  10. Download and analyse engine data if applicable. Address any anomalies before the next flight.

 Flight 2

  1. Repeat steps 4-10. Remain aloft 30-60 minutes unless you note any abnormality.

 Flight 3

  1. Repeat Flight 2, except…

  1. Cruise climb at least 10,000 feet AGL, (if permitted) still over the airport. Ensure manifold pressure, fuel flow, temperatures and pressures indicate as expected during the climb.

  1. Fly in the vicinity of the airport for 60-90 minutes. Follow engine break-in directions. Vary manifold pressure (in airplanes with controllable speed propellers) and propeller speed occasionally.

  1. Repeat steps 9 and10.

 If the engine is fitted with a turbocharger, make another flight: 

Flight 4

  1. Repeat Flight 3, except climb to 17,500 feet MSL (assuming a turbocharged/turbo-normalised “altitude engine.”)

  2. Repeat Flight 3 again, except climb to above Critical Altitude (usually around 18,000 feet, again assuming an altitude engine).

 We aimed for between five and six hours of post-production test flying using this profile. If the engine-break-in instructions indicate the engine is not yet broken in by this time (which I expect is unlikely), add additional flights as needed. 

 I did not want to get far from the airport until I had done at least this much with a new or newly modified engine. It may seem excessive, but although I did have several problems arise during engine check-out I never had an anomaly without being able to immediately return and land. Certainly I would not want to launch into instrument or night conditions, or out over the mountains, deserts or large bodies of water without logging at least five hours ... on a new, overhauled or modified engine, or with a newly installed cylinder.

Being in command
 of an airplane means staying ahead of potential problems during high-risk operations. Certainly, the first several hours of flight after a major engine work qualify.  When you accept an airplane after engine repair or modification you are a “for-real” test pilot.



Tony Birth