>Disclaimer:
I am not an engineer nor an aircraft technician. I used to work in the heavy process industry and my job entailed maintenance of heavy industrial equipment. I have since left that industry and have not been working in such an industry for more than 10 years.
As such, my opinions given in this article are strictly from a maintenance viewpoint, and not from an operator’s (ie the pilot) or engineer’s (which includes design) perspective. Furthermore, readers are advised to note that 10 years is quite a long gap, which means maintenance practices may have changed drastically. OK, you may now read my article with a dose of salt, because I have never maintained any aircraft in my life.
The Explanation
The explanation given for the downed Apache is that it was caused by an anti-ice start bleeder valve (AISBV). Of course, I don’t have the maintenance manual of the Apache to be able to see how that can be the case. The closest I got can be found in this link. Quite a good explanation on how the anti-ice system works, but not enough to tell how a corroded bleeder valve can down the Apache.
I found another link, which also makes good reading. That’s because one of the forummers, named Gremlin29 in the thread, is an actual Longbow pilot. His experience and the information given throws more light.
Posted by Gremlin29 on first page:
Normally yes. There are conditions where sustained single engine flight may not be possible but this aircraft isn’t armed and doesn’t have the FCR installed so it should have had plenty of power.
Just so you don’t think I’m arguing for the sake of arguing I am a Longbow pilot (currently serving) and have a pretty good understanding of how these aircraft work. There are numerous ways the pilot can induce dual engine failure or simply misdiagnose a malfunction which in turn could create a bigger emergency which does happen. A dual engine failure not caused by the pilot or combat operations will be a first from what I have been told. That said, this is a complex aircraft and there are far too many things to list as potential causes. We will learn the cause in the not too distant future.
On page 2 from Gremlin29 again:
This is a curious situation and I will be careful here. The AISBV (anti-ice start bleed valve) will not cause an engine to shutdown. The odds of two unrelated components failing at the same time is incredible. The valve is either open or closed, and failure in a partial open/closed condition will not cause an engine to fail. They can corrode if the engine wash is not performed correctly, the chemicals involved are very corrosive but that’s besides the point that this valve isn’t going to cause an engine failure. They simply use bleed air scavanged from the engine, I don’t even think they could even cause a compressor stall if you tried (pilot can eliminate compressor stall quickly and easily).
If both engines failed they would autorotate. If they had a single engine failure and could not continue flight they would perform a rolling landing touching down at or above minimum safe single engine airspeed. This airspeed is not a fixed number, but is typically rather low, say less than 45 knots. Aeordynamic breaking will stop the forward roll, looks to me like they had a slow rotor with little or no pitch when they pulled aft cyclic to brake the aircraft. That’s my spin on it.
The Apache has two engines. What Gremlin29 is saying is if we were to take the story that it was downed by the bleed valves, BOTH the valves must fail at the same time for both engines to fail.
Gremlin29 again:
To give you an idea of what a non-emergency a failed AISBV is, there’s not even an emergency procedure for it. It is a fairly simple device, installed on each engine and they operate independently. That’s why I find the whole thing curious, because there’s really no practical reason for them to both fail at the same time, the odds are just incredible. They can be turned on or off, or placed in manual or automatic mode. They can be turned on or off independent of each other.
To me, from a maintenance perspective, Gremlin made a very significant point. If there is NO EMERGENCY PROCEDURE for bleed valve failure, that to me indicates that bleed valve failures cannot down the Apache.
If it can down the Apache due to bleed valve failure, it means only one thing – the manufacturers have negligently left that important emergency operational procedure out. But that is highly unlikely. As such, I tend to agree with Gremlin that anti-ice start bleed valve failure won’t down the craft.
But what if AISBV was the cause? -
Please note that I am giving my opinion from the maintenance perspective and NOT from a designer’s perspective. It must also be remembered that I am giving my opinion simply based on whatever information I get over the internet and NOT from the technical manual of the craft.
If we were to believe that the AISBV was the cause, then I can think of only one way how it could have happened. Could there have been a “fail safe” device that is tied into the operation of the AIBSV?
A fail safe device operates such that if there is an event of a failure of a crucial instrument or equipment, the whole equipment would be put in a “safe mode”, such that personnel and equipment would not be harmed, or harm is minimized.
As an example, if a the cooling system of a machine fails, the machine would stop operating to prevent overheating.
Problems with Fail Safe Operations -
At best, if fail safe operations malfunction, it causes inconvenience. For example, someone designs a seat belt to “fail safe” such that if the driver is not buckled up, he cannot start the car. This ensures that the driver would never be able to drive off without buckling up. However, if the sensor on the belt is faulty, even when the driver belts up, the instrument would read as “unbuckled” and the car won’t start. This is unnecessary inconvenience.
At worst, sometimes due to design fault, it can cause major damage to equipment and even endanger lives. This may sound very basic and stupid, but I have seen how designers, due to carelessness or negligence, fail to foresee the dangers.
Again, using the seat belt example. The fail safe operation should ONLY WORK when the engine has NOT YET STARTED. However crazy and unlikely this may sound, there is the rare occasion where the designer of a fail safe feature overlook that once the machine is in operation, the fail safe device must not function IF shutting down the equipment means loss of control such that it endangers lives.
Imagine the sensor at the seat belt buckle fails when the car is already on the road. If the fail safe device were to kick in, it would cut off the car’s engine, endangering the driver and other road users.
Needless to say, the above if occurs, is a design fault which the manufacturer would be liable for damages if any harm is caused. Unlikely as it may sound, I have come across a couple of times newly designed equipment having such design problems.
So was it caused by the AISBV or not? -
According to Gremlin29, who is a pilot of an Apache, it is highly unlikely. According to Teo Chee Hian, it is.
But for the AIBSV to fail such that it can down the Apache, it has to mean that there is some kind of trigger mechanism such that if it fails, it would shut down both engines.
I don’t have the Apache operation or Maintenance Manual. So I can’t tell if AIBSV failure can cause the downing. Whatever it is, I am more inclined to believe Gremlin’s opinion that it cannot be the cause. That’s because for AISBV failure to be the cause, there has to be a fail safe device, and that fail safe operation if kicked in, would shut off both engines in mid air!
A very unlikely scenario which means that there would have to be a major design fault, if we were to believe Teo’s version as reported in the media.
