“I am inclined to suspect that a vapour lock may have caused the engine to lose power.”
(This report was compiled in the interest of the promotion safety and not to establish legal liability.)
Date of Accident: 22 December 2010
Time of Accident: 15.20Z
Type of Aircraft: Cessna 172 K
Type of Operation: Private
Pilot-in-command Licence Type: Private
Licence Valid: Yes.
Pilot-in-command: Total Flying Hours 503.3 Hours on Type 459.2
Last point of departure: Kitty Hawk, Next point of intended landing Kitty Hawk
Location of the accident :Welbekend East of Pretoria in a corn field. Meteorological Information Surface wind: 340/20kts. Temperature 28C. Number of people on board: 1 + 0
No. of people injured: 1 No. of people killed: 0
History of Flight:
The aircraft took off from Kitty Hawk Aerodrome on Runway 01 at 1500Z. Prior to takeoff the pilot performed the engine run which indicated that the magnetos were within the required limits as. After two circuits and landings the pilot flew towards the South-South-East of the Aerodrome.
After seven minutes, at approximately 400 feet AGL, the engine started running rough. The mixture was rich, the pitch full fine and manifold pressure was 22”. The pilot switched on the fuel pump but it had no effect.
The pilot selected a field to his right that was planted with maize approximately 250 mm high. The ground was wet as the area had had more than 100 mm of rain over the previous three days. The wheels sank into the ground and the nose gear broke off. The plane flipped onto its back.
Unsuccessful forced landing due to engine failure because both magnetos were earthed via bad condenser leads.
Aircraft Information: Type Cessna R172K Serial Number R172-2764 Year of Manufacture: 1977. Total Airframe Hours (At time of Accident) 1920.1 Last MPI (Date & Hours) 28 July 2010 1919.2 Hours since Last MPI 0.9. C of A issued 28 February 1978 C of R issued Date 13 May 2008
Type Continental IO360K Serial Number 355844 Hours since New 1920.1 Hours since Overhaul 89.8
Tests and Research:
The magnetos were sent to an approved AMO for further investigation. The report states: Right hand magneto S/N A189372 Checked timing and rotation of Magneto and found satisfactory. Inspected condition, found one tower spring missing on harness. Found arcing on same lead pin. Found the condenser lead in bad condition, wire touching magneto frame and braid giving “dead magneto.”
Left hand magneto S/N A189374 Checked timing and found satisfactory. Condition inspected and found condenser lead in a bad condition, wire touching frame giving a “dead magneto”. Harness found to be satisfactory. The engine was taken to an approved maintenance facility for dismantling and inspection. During the investigation it was found that pistons no.2 and no.4 showed a signs of detonation. Melted aluminium piston heads grinded metal pieces caused the oil filter to block, causing the by-pass to open, which in turn sent unfiltered oil to the bearings, which in turn caused the seizure.
Teledyne Continental Motors, the manufacturer of the engine, issued a service bulletin M77-3 which states: TCM does not recommend or authorize the use of automotive fuels in any of their aircraft engines. The engine warranty and pro rata policy will be voided if such fuels are utilised. Fuels must conform to ASTM-D910 or MIL-G-5572E, if satisfactory engine service life is anticipated. Automotive fuels can contain additives that act as corrosive agents, formulate gum deposits and therefore increase combustion chamber deposits. Continued operation on automotive fuel can lead to detonation, pre-ignition and sticking or eroded valves. The vapour pressure of automotive fuels exceeds that allowable for aviation fuels. The increased vapour pressure increases the tendency to vapour lock at higher altitudes. A vapour lock condition can cause complete power loss. The use of any fuel that does not conform to the above specification may cause cylinder assembly, valve, piston and/or piston ring damage/failure.
According to the pilot, for the 23 hours before the accident, the aircraft was using automotive fuel. The aircraft did not have a supplemental type certificate (STC) to use the automotive fuel. The investigation revealed that the engine power loss and the subsequent engine failure were as the result of a wire touching the magneto frame and braiding, with the result that no spark was produced. Although further investigation revealed that pistons no.2 and no.4. were worn out/ damaged, this was not a factor in the engine failure.
The aircraft was flown approximately 0.9 hours since the previous MPI. It was revealed that both magnetos were earthed, therefore it appeared that the AMO did not install the magnetos properly, resulting in chafing of earth wires, which led to an engine failure. It is recommended that the AMO should be addressed in this regard.
This is the most extraordinary accident I have seen in a long time. Behind the CAA’s usual stuff-ups it hides some interesting and complex safety issues which I am battling to come to terms with.
Bear with me, we will run through the facts first and then look at the implications for the average pilot.
First, this was the initial flight after an MPI – statistically the most likely time for mechanical failures.
What I see here is the owner’s attempt to save money at every turn. The most obvious example is using automotive fuel instead of Avgas without the STC. I have a feeling that this may have been the direct cause of the accident. With a density altitude of around 8000’ on that day, I am inclined to suspect that a vapour lock may have caused the engine to lose power.
The CAA’s conclusion that earth wires (or ‘P’ leads) on both magnetos just happened to short out at exactly the same time is ludicrous. The photos show that these leads suffered years of wear and abuse.
The logbooks tell us that when the engine failed, it had only done only 89.9 hours since a complete overhaul, and less than one hour since MPI. Frankly, I don’t believe a word of it – and neither should the CAA. The engine was in shocking condition both internally and externally.
Internally, detonation had caused two pistons to be ‘worn out/damaged’ so badly that the debris from them had completely blocked the oil filter and then circulated through the bypass so that it caused the bearings to seize. For those who are not mechanically minded this means the engine was about to disintegrate, and that it was in need of another complete overhaul.
The fact that the filter was totally blocked means that it had not been changed at the MPI, which should have happened. In other words the AMO was not doing its job.
A tower spring in the distributor section of one magneto was missing. It’s just possible that this could have been forgotten during overhaul – but a glance at the condition of the condenser leads tells us that the magnetos were overhauled only in the logbook – but not in the real world.
In short, the AMO was operated by a bunch of crooks. Further, I would suggest that the owner was complicit in the fraud. Any pilot with half a brain cell would have seen from its condition that it had not been overhauled. Methinks (to use a lovely Shakespearian word that’s coming back into fashion) that the owner and the AMO agreed to simply overhaul the logbooks, without touching the engine. Or to use another term that is in vogue at the moment – they opted for a ‘virtual’ overhaul.
But it gets worse. There is something very fishy about the history of this aircraft. The logbooks say that it is a ‘K’ model built in 1977 – but that can’t be true because Cessna stopped fitting Continental engines to their 172s nine years earlier in 1968. So this aircraft should have had a Lycoming engine. The CAA could have obtained this information from Google, as I did.
What can we learn?
This is where I normally give you some pithy bullet points of dos and don’ts, but with this accident I am left scratching the pip – and I’ll tell you why.
I recently refused to fly a Piper Arrow because the quick release cowling fasteners had been wired shut. I made a fuss about it until the owner agreed to let me undo the wiring and remove the cowl. That’s one of the things I really like about the Piper range – it’s easy to inspect the engines. It turned out that this engine was in great condition and I was very happy to fly it.
But this is rather a silly story because I have to ask myself whether I would have done the same on a Cessna or a Mooney? Obviously no. It’s simply not possible to inspect the engine properly on most light aircraft. The best one can do is shine a torch in through the oil filler hatch and try to get a general feeling for the engine’s condition.
So, inspecting the most mechanically suspect part of any aircraft – the engine – turns out to be the most difficult.
All I can do, is suggest that you become a mechanical detective. This is easy if it’s an aircraft that you fly regularly. First, have a critical look at the logbooks. If the owner doesn’t want to show them to you, then take your business elsewhere. Once you’re satisfied that everything is legal and up to date then a general look around will tell you a lot.
Oil leaks are the first sign that things are not great – unless you are flying behind a radial engine or a Gypsy, in which case a lack of oil leaks probably means a lack of oil. Just feel under the belly of the aircraft – that’s where the oil winds up if it’s leaking. If your hand gets oily, go and fly another aeroplane.
Strangely, the outside of the cowling can sometimes give you useful information. Blistered or scorched paintwork may indicate leaking exhaust pipes, blown gaskets or troublesome turbochargers.
If you use a torch you should be able to spot any obvious faults like frayed wires, torn elephant trunk hoses or fluid leaks.
If the outside of the engine looks good, the only way you will get some info about its inner workings is to have a look at the oil. That is the life blood of the engine. If it is changed regularly then it should have a pretty honey colour. Black, or dirty grey oil is not necessarily a don’t fly flag, but it calls for the raising of an eyebrow. The owner should be able to explain that it’s the type of oil being used, or have some other good reason for its appearance.
Finally, the history of the oil level is important. Is the engine’s consumption in line with the expected use shown in the POH? Excessive consumption is a big red flag.
In a nutshell, if it’s a one-off flight you had better be a damn good mechanical detective. If it’s an aircraft you fly regularly, you can take some comfort from its history. And if it’s a Piper – well there you go. Not that I am biased at all.