PlasticPilot.net

Yes, this is your favorite aviation blog, even if this post title sounds much more like the typical anoucenement for a patch for a mysterious software. Apparently, the problems with the Eclipse 500 Very Light Jet FADECs is now solved.

The FADECs software did crash when it received an out of range value from the trhottles. According to AvWeb: “Eclipse says its solution will increase the range limit of the throttle quadrant assembly to prevent the fault condition from occurring.” Given the kind of problem - both FADECs failing at the same moment, when throttle is pushed full forward - this is not really a surprise to me.

Eclipse will deliver a software update that will remove the problem. It is not the first time in aviation history that a software patch will solve a problem, but given the mediatic buzz around the VLJs, and the Eclipse 500 in particular, this is gets more coverage than an Airbus patch.

The name of the patch I mentionned in this post is a personal inventon, trying to be fun, and to make you think. The serious problem that affected the Eclips will be solved by simply uploading a new firmware. I don’t know however if the Eclipse interface uses USB or Bluetooth.

Jokes put aside, I know many pilots that will feel uncomfortable with the concept of flying a software controlled plane. Most of them associate “software” with their own experience at home, with their PCs. Airplanes are not all the same, airlines are not all the same, and software are not all the same.

The development standards, and quality of software used aboard aircraft has nothing to to with what you have in your PC. The hardware is also different, and there are no third products that you can download yourself in the FADECs, making the environment much more controllable.

Another thing that make software sounds mysterious (and then dangerous) is that most pilots don’t understand exactly what it is, how it’s made, how it works, and what it does. A magneto, alternator or carburetor is much easier, and these things can be seen, touched, examined, dismantled, and inspected. You can’t do that with software.

Shall we get rid of software in our planes ? Hell NO ! There is no efficient engine management without electronics and software. There is no GPS, no RNAV tools without software. Without software, no cockpit integration is possible. Things like TCAS, GPWS, Mode-S transponders, FMS, and many others are all software based. Did I mention autopilots ?

As any airplane part, software can fail. It’s not because something is computer-based that there will be more or less failures. Just like a crankshaft, pump, belt, servo, landing gear assembly, fuel line, piston, windshield, voltage regulator, intercom, or any other mechanical or electrical component, software can fail.

This is exactly why there are so many different computers on board. For engines management, avionics, navigation, and so on, each system uses its own, separate hardware and software, to avoid crashing all of them at the same time. That would be bad. At least as bad as a failing wing-root, or a lost engine making the plane out of balance.

So please don’t be affraid of software simply because it can’t be seen or touched, and don’t compare aircraft embedded software with “quickly downloaded - quickly deleted” kind of stuff that fulfills most harddisks. Software is the next step in aviation, just like voice replaced morse code, and composite slowly replaces aluminium.

With the highly demanding validation and certification standards required in aviation, the risk levels remain minimal. Not zero, but well acceptable. Remember that safety is not defined as the absence of hazards, but the absence of unacceptable hazards.

Thielert engines have been around for quite a while now - my personal flight time on Thielert equipped planes is close to 68 hours over two years. As far as I’m concerned these engine perform well. The only negative feed-back I can think of is about the high pressure pumps the engine uses to bring Jet-A1 fuel to the temperature and pressure conditions which make it explosive. The fuel is injected under a pressure of 1350 bars and at a temperature of 120 °C !

The planes I flew - a DA40 TDI and a C172 retrofit - both had some troubles related to the high-pressure pumps, which make me think that the pump could be the weak point of the Thielert engine, even if the troubles were of different nature.

No fuel starvation allowed
In a previous post I mentioned that the club I used to rent the Cessna from decided to forbid us to fly side-slips. This is decision was an extension of the AFM which mentions that side-slips with low fuel levels are forbidden. The reason is that the high pressure pump can be damaged after a fuel starvation of 15 seconds ! A prolongated side-slip could lead to such a condition. Any engine would probably stop running under such circumstances, but the pumps (electrical and mechanical) would not be damaged !

No water allowed
A DA40 also had its pump replaced because, according to Diamond, it had been damaged because too much water went through it. The hypothesis is that because of massive condensation and insufficient pre-flight draining left water in the tanks. It is not clear to me yet how water instead of fuel can be so bad for the pump, but I’m not an engine specialist.

Starting problems
One of the operational advantages of FADEC controlled engines is that they always start easily and at first attempt. No three hands procedure needed, nor variants for warm or flooded engine. Just press start or turn the key, and the engine fires-up… says the theory.

One of the planes I rented a lot was just unable to start when the engine was warm. A minimum cooling time was required before any successful restart. It went to the maintenance workshop several times before Thielert accepted to replace the full engine (or pump, I’m not sure now…). Measurements (the good side of FADEC controlling everything) shown that the pump was not able to reach the 300 bars needed during the starting phase.

Youth problems
None of these issues cause any engine failure in flight nor any incidents. Unexpected maintenance is always exasperating, but seldom dangerous. These problems are certainly youth problems that Thielert will cure rapidly. Don’t forget that the last “evolution” before diesel engines was injected engines ! And as far as I’m concerned, Thielert engines perform well.