PlasticPilot.net

On the 5th of June, an Eclipse 500 was about to land when it experienced a windshear. The pilot applied full power to counteract it. After touchdown, the plane accelerated, with both engines delivering full power, and the crew was forced to take-off again.

Both engines were still delivering full power, and both FADECs were reporting failure. The Quick Reference Handbook (QRH) do not mention procedures for a double FADEC failure, but says that if a FADEC is failed, the corresponding engine must be shut down.

The crew decided to shut the right engine down. After that, the left engine stopped delivering thrust, remaining at idle power, whatever the throttle position. The crew achieved to land, kudos for that, and this hopefully happened in VMC conditions.

Each FADEC is made of two channels, and if one fails the second one takes over. If both fail, parameters are taken from the other engine. If the other engine FADEC is also failed, the last known parameters are kept. As both FADECs failed simultaneously, the engines continued to deliver maximal thrust. After the right engine was stopped, its FADEC was no longer reporting failure, so the left engine FADEC “copied” its parameters, leading to idle thrust.

The system behaved as designed, and if it allows for more redundancy that classical (electro-mechanical) systems, in that particular case, it failed almost completely. The open question is why pushing the throttles to a full forward position causes a double FADEC failure..

On request of the NTSB, Eclipse did upgrade the AFM and QRH to inlcude a procedure to handle such an even, and the FAA mandated an inspection of the throttle assembly of all Eclipse 500 aircraft. Read more from Eclipe, and from NTSB.

The problem could be reproduced (on the ground), and the FAA issued an airworthiness directive requiring an inspection of all Eclipse 500 aircraft before their next flight, and inclusion of the new procedures in AFM and QRH. This inspection can be performed by the pilots themselves, and simply requires to turn electrical power on and push the throttles forward, looking for any FADEC alert

When evaluating the value of an aircraft, one of the key factor is the TBO: Time Between Overhauls. Engine and propeller manufacturers define maximum time-in-service. The closer the engine / propeller is to this maximum age, the lower the plane value. This is rather logical, as the new owner will have to replace them sooner as if the time in service was lower.

This TBO story could be simple, but rules (both FAA and JAA) gives some flexibility to private owners and operators. As this includes all non-commercial operations, flying clubs can rent aircrafts which fly beyond their engine’s TBO. This is the open door to an interesting debate: on time maintenance vs. on condition maintenance.

On one side, the “on time maintenance” clan. Engine reaches its overhaul time ? Replace it by a new one. Dot. There is a reason why manufacturers define a limit, isn’t it ?

On the other side, the “on condition maintenance” clan. Basic rule: why replace an engine that runs well ? Obviously, “runs well” do not simply means starts and operates well. A serious “on condition maintenance” policy it typically based on things like:

• How the engine has been operated
• What kind of maintenance has already been done
• Oil and oil filter inspection
• Compression reports
• Spark plugs inspection

The required analysis are not for free, but they remain low when compared to the cost of a new engine. Because of my technical background, I’d tend to prefer on condition maintenance… if I only could afford to own a plane

Thanks to their black-box / monitoring role, the FADECs do help to gather information about how the engine was operated, and about general engine condition… but not for the Thielert engines. The Thielert maintenance plan calls for an inspection at 1′200 hours, and replacement at 2′400. No other way - not even a full revision.

One of the reasons is that given the high pressures within diesel engines, they are made of a single bloc of metal. It’s not possible to replace just a cylinder, as some do with classical engines. This leads directly to the second argument in favor of “maintenance on condition”: most defective engine parts will fail within the first hundreds of hours. Why introduce the risk of “youth problems” in an engine that ran well for several hundreds of hours and gives no sign of trouble ?

I should may be ask an aviation lawyer, because the exact consequences of an incident with an engine flying legally with a post TBO engine are not clear. If you have any hints on this, or more generally on this topic, feel free to comment !
Read more on this topic:

Aircraft Maintenance Technology online

AvWeb Columnist Mike Busch, fan of overhaul on condition

Thielert Centurion engines (search for TBO)

For the last years, the Jet-A1 piston engines makert has been dominated by Thielert with its Centurion family. Another german company, Zoche, achieved to create some buzz, but unfortunately none of their engines got certified yet (read here).

With Cessna and Diamond using their engine, Thielert is in a good position, and even the French SMA is in a position to endanger Thielert’s monopoly. Until now the most credible concurent is the new engine being developped by BMTech together with Diamond.

However this could change soon. According to avweb.com, Teledyne Continental’s new President Rhett Ross anounced company’s comittment to develop a diesel engine to be certified by the end of 2009. A prototype shall be demonstrated in late 2008. The new engine should be in the 300 HP range, making it a serious candidate for high-performance single engine like PA32, Bonanza, and C210.

With one of the two major gasoline piston engine manufacturers entering the diesel / Jet-A1 powered engines market, it is clear that even the US market will slowly move to this new technology. It started in Europe because the price of AVGAS became a prohibitive factor well in advance, but now that even the US is affected by this, aero-diesel engines have a bright future !

When it all started years ago, the DA40 TDI was the sole plane available with a diesel engine. Then came the C172 retrofit, the C172-TD, and now this engine from Continental. When a PA28-TD and Lycoming engine will be available (who knows…), the whole single engine plane market will be covered, and I will no longer look like the strange guy flying the strange planes.