After COVID-19
A safe return Francis Donaldson discusses some sensible precautions to take when we can get back to our aircraft once the lockdown allows
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s this goes to press, with the nation still in lockdown, many LAA members will be wondering about their aircraft sitting long unflown in their hangars, and what will be needed to return them safely to flight when freedom of movement returns. We hope this practical advice can ensure your aircraft is in a safe and airworthy state when the COVID-19 quarantine restrictions are relaxed. More detailed advice can also be found in Technical Leaflet TL 2.32 and, if your aircraft is in need of a Permit inspection, additional advice can be found at: https://tinyurl.com/permit-fly. In fact, provided it has been properly covered or hangared, most aircraft can withstand a short period of inactivity without too many problems. After all, despite the best of intentions, many of us don’t get to fly over three or four months during the worst of winter, yet we take few special measures to tend to the engine or airframe either during this time or on its return to service. Please, don’t just ground run During this period of inactivity, about the worst thing you could do would be to give the engine a short ground run. This is unlikely to get the oil hot enough to drive off moisture, encouraging condensation to pool in pockets within the crankcase and other expensive components, which can exacerbate internal corrosion. Realistically, the only way to get the engine sufficiently hot is to fly it – probably for at least half an hour. If you can’t do that, don’t run the engine at all. Internal corrosion will be minimal in most engines, there’ll be a thin layer of oil, forming a protective internal varnish-like coating on all surfaces thus affording them protection. There are some exceptions though. After being left unused for many months, Lycoming engines can have cam problems, especially if using straight oils without any corrosion inhibitor. The cams are only splash fed and over a long period of being static, the oil film between the cams and cam followers can break down. This can lead to rapid cam and follower wear in subsequent running. Products such as Camguard can be used to help protect the cams and cam followers on Lycoming and similar engines, but mustn’t be used on an engine that’s running-in using a ‘straight’ oil because the extra lubrication will prevent the engine ever running in successfully. If using a ‘W+’ oil or multigrade then there’s little benefit, if any, in using additives as they already include cam and anti-corrosion additives. Four-cylinder Rotax and Continental engines, with their underslung camshaft arrangements, don’t seem to suffer the same cam problems, especially if running on oils with anticorrosion additives. The venerable de Havilland Gipsy Major engines suffer from a special form of corrosion problem as
Above Fuel should figure highly in your checks. Is it stale, is it clean, are there any leaks, are the filters clean, are the hoses and pipes sound? A fuel problem is probably the most likely of issues an aircraft could exhibit following lengthy inactivity. Inactivity not being something Wg Cdr Chris Pote had on his epic trip to NZ 18 months ago!
moisture is deposited inside the crankshaft, which is in effect part of the oil filter system, and corrodes the crankshaft from the inside. This creates stress concentrations which can trigger fatigue cracking. The hollow big ends on Gipsy-type engines act as centrifugal filters, and once water gets in there is no way for it to escape unless it is boiled off by running in flight. To turn or not to turn? There’s always debate over the advisability of regularly turning by hand the propeller of an aircraft that’s static, perhaps on a weekly basis. Followers of this mantra suggest that this will help keep oil spread over the length of the bores, cam and bearings, and perhaps avoid corrosion developing where moisture might gather over the top piston rings. And, by avoiding just one or two inlet and exhaust valves being open for the whole time the aircraft is out of use, corrosion of the valves and seats on those valves might be avoided. Also, the chance of any corrosion developing on the valve stems might also be reduced and any corrosion tendency more evenly shared amongst the bores. Unfortunately, there’s a counter-argument that turning the prop might tend to wipe off the oil film on the surfaces of the parts, promoting corrosion. We suspect that there’s no simple answer, and this is a good reason to refer to your specific engine’s maintenance manual or your LAA inspector for type-specific advice. Fuel When it comes to re-commissioning the aircraft after the lockdown, one aspect that will need to be considered carefully is the contents of the fuel tanks. Mogas is expected to have a short operating life, around three months maximum, in a road vehicle. ‘Stale’ mogas may have evaporated away some of its octane-
12 | LIGHT AVIATION | May 2020
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