AH64-D Longbow of RSAF downed. what could have caused it?

M1Brams

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An Apache helicopter from Singapore's air force crash-landed in an open field in a residential district on Thursday but no-one was injured, the defence ministry said.

"A Republic of Singapore Air Force Apache AH-64 helicopter has made an emergency landing... There has been no damage to civilian property or injury to personnel reported," the defence ministry said in a statement.

An AFP photographer at the site said the tail of the light attack helicopter had broken off from its main body and was lying about 70 metres (yards) away.

About a dozen air force engineers clad in black uniforms were sifting through the debris and a crane stood by to clear the rubble, he added.

A witness told the Straits Times newspaper the helicopter had circled in the air and descended rapidly before crash-landing on the barren field.

The Apache AH-64, built by US aviation giant Boeing, is a four-blade, twin-engine attack helicopter, and is used by the US, Israeli and Japanese militaries, among others.

Singapore has one of Asia's most advanced armed forces, and regularly takes part in military exercises with regional countries as well as the US and China.

The tail rotor split from the airframe after crashing into the field.


early speculations are engine failure causing the pilot to use autorotation.

what could have caused this?
 

Gremlin29

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what could have caused this?
There's a laundry list of potential causes however the story doesn't provide nearly enough info to even begin speculating.

Dual engine failure is however not a likely candidate because throughout the entire life of the Apache program, none have had to autorotate due to a dual engine failure (excluding combat operations involving shoot downs).
 

M1Brams

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There's a laundry list of potential causes however the story doesn't provide nearly enough info to even begin speculating.

Dual engine failure is however not a likely candidate because throughout the entire life of the Apache program, none have had to autorotate due to a dual engine failure (excluding combat operations involving shoot downs).
i guess its sparse, owing that it just occured. am trying to find out more information of the incident
it happened around late afternoon today, Singaporean time .

Looks like the pilot did land belly up, saving the blades at least for the main rotor which is quite

as to the cause i dont think an apache would just fail with regular service maintenance. However as to what happened to the airframe before or after the incident is abit mysterious if the airframe or tail rotor did just seperate from each other in mid air.
 

Kilo 2-3

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i guess its sparse, owing that it just occured. am trying to find out more information of the incident
it happened around late afternoon today, Singaporean time .

Looks like the pilot did land belly up, saving the blades at least for the main rotor which is quite

as to the cause i dont think an apache would just fail with regular service maintenance. However as to what happened to the airframe before or after the incident is abit mysterious if the airframe or tail rotor did just seperate from each other in mid air.
Had it broken off in mid air, we'd be looking at a lot more pieces in that picture, most of them very, very small. The helo pictured here is fairly intact. Secondly, a mid-air failure probably would have scattered the tail component fairly fair away from the fuselage/cockpit crash site. Thirdly, mid-air separation with the main rotor would cause the cockpit/fuselage section to spin, which would probably have sheered off the landing gear and possibly the hardpoints on impact.

None of these are the case here, which leads me to believe that the breakup happened on impact. The only thing which I can think of to counter this theory is the lack of major trauma to the ground, something I'd associate with an impact hard enough to break up an AH-64.

My guess would be the pilot autorated into the ground at a fairly high rate of descent, and the ensuing impact with the ground broke the Apache's back.

I'm no air crash investigator; but that's my layman's opinion of the issue.
 

Gremlin29

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I agree, the tailboom did not break apart in flight which is evident in the photo.

I would "guess" the tailboom seperation is due to a blade strike. If he hit hard enough to break the boom in that location the main landing gear would have stroked and the gun would likewise "probably" have stroked into it's crash box plus or at the least, it would be covered in dirt and sod. It's a weird place for the tail boom to just break anyway, even after a hard landing and it doesn't look like this puppy hit that hard.
 

OPSSG

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Guys, see Mike Yeo's blog for more pictures and details for the RSAF Apache crash and to David Boey's blog, which has more details here. These links maybe of help in your discussions here. David by the way, is an inactive member of our forum, and goes by the handle Chinese Junk.

David was one of the first, if the not the first reputable source, with the news and he initially posted that the crash was believed to be multiple engine failure. However, that is speculative. See the above links for more details.
 
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M1Brams

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Guys, see These links maybe of help in your discussions here. David by the way, is an inactive member of our forum, and goes by the handle Chinese Junk.

David was one of the first, if the not the first reputable source, with the news and he initially posted that the crash was believed to be multiple engine failure. However, that is speculative. See the above links for more details.
thanks OPSSG. i read the straits times this morning and it was speculated to be multiple engine failure. Mindef has just also released an article on the said crash and it does, as of now, looks like it.


An RSAF AH-64 Apache helicopter made an emergency landing in an open field between Woodlands Ave 12 and Woodlands Dr 64 at about 1530 hrs today.

The helicopter was on a routine maintenance flight when it encountered engine problems. As an emergency drill, the pilots chose an open field away from buildings and populated areas to make an emergency landing. The tail section of the helicopter was damaged during the landing. Both pilots are unhurt. There is also no damage to civilian property or injury to personnel.

An RSAF response team led by BG Wong Huat Sern, Commander Participation Command, is on site to manage the situation and recover the aircraft.

Edit: Mindef News release here.
 
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M1Brams

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thanks OPSSG. i read the straits times this morning and it was speculated to be multiple engine failure. Mindef has just also released an article on the said crash and it does, as of now, looks like it.


An RSAF AH-64 Apache helicopter made an emergency landing in an open field between Woodlands Ave 12 and Woodlands Dr 64 at about 1530 hrs today.

The helicopter was on a routine maintenance flight when it encountered engine problems. As an emergency drill, the pilots chose an open field away from buildings and populated areas to make an emergency landing. The tail section of the helicopter was damaged during the landing. Both pilots are unhurt. There is also no damage to civilian property or injury to personnel.

An RSAF response team led by BG Wong Huat Sern, Commander Participation Command, is on site to manage the situation and recover the aircraft.

Edit: ].
Thanks alot OP. With regards to this, i believe the Seahawks
and the AH64D's of the RSAF will be grounded? Will there be any feedback to the US? if necessary?
 

OPSSG

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Thanks for keeping the forum updated and your interest. You are unable to post links until you have completed 10 posts and this spam control measure was instituted because there were too many spammers who tried to hawk their wares here.

As a precaution and in the latest release, Mindef has announced the following:

"RSAF will temporarily suspend all training for its fleet of Apache AH-64 helicopters pending the outcome of the investigation. Training for the RSAF's Sikorsky S-70B Seahawk naval helicopters, which have similar engines as the Apache AH-64 helicopters, will also be on hold."​

So evidently, the incident was could well be caused by engine problems. It's too early to tell what is the exact cause, as I'm sure there will be a board of inquiry convened and if necessary, for flight safety, the RSAF or Boeing will update the US Army Aviation on the relevant findings via a technical note.

Edit: More video, pictures and news from the Apache crash landing site at the link provided. This could be terribly inconvenient as Ex Wallaby 2010, in Shoalwater Bay, Australia, is ongoing. F-16s, Super Pumas, Chinooks and Apaches are also scheduled to participate in that armour exercise. This year's Ex Wallaby is the biggest and longest ever, with 6,000 Singapore troops participating in that armoured exercise and grounding Apaches would affect the combined arms portion of that exercise. SIA (or such other chartered commercial jets) has around scheduled 18-19 charter flights to Rockhampton Airport for troop ferry.
 
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Gremlin29

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If they experienced non-pilot induced dual engine failure, it's a first for the Apache and I'll be extremely surprised.
 

M1Brams

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If they experienced non-pilot induced dual engine failure, it's a first for the Apache and I'll be extremely surprised.
Looks that way,with the initial reports. Umm.. in the event of a single engine failure is the Apache able to continue on its other engine?
 

Gremlin29

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Looks that way,with the initial reports.
The initial report report says "engine" as in singular.

Umm.. in the event of a single engine failure is the Apache able to continue on its other engine?
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.
 

OPSSG

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With regards to the Apache AH-64 Helicopter Emergency Landing, Deputy Prime Minister and Minister for Defence Teo Chee Hean has released the following statement:

"I have been receiving regular updates from Singapore. Our preliminary findings are that a mechanical problem was the cause of the incident. We are conducting investigations together with the manufacturers of the aircraft. Our preliminary findings also show that designated flight routes and emergency procedures were followed and these allowed the pilots to land the aircraft in an open field. Our next steps are to make sure that we do a thorough investigation to find the root cause. We will thoroughly inspect our Apaches and Seahawks before any decision is made to resume flying of these aircraft."​
 

Toptob

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Looks to me that bird took a serious impact. But it says the crew is unhurt, and the damage seems puzzling to me. How could the tail of an apache break off in general (I guess there's many explanations to that).

From what I see on the pics, the tail broke off and the apache rolled some distance on its wheels. But I dont see a trail on the grass where the fuselage would have been dragged, just wheel marks. And I would imagine that when a helicopter crashes so hard that its tail breaks there would be more damage on the fuselage, and on the tail section.

@ Gremlin
I would "guess" the tailboom seperation is due to a blade strike.
I'm no expert so I'll defer to your knowledge, but how would it happen that the rotor (the main one I presume) would hit the tailboom? Undoubtedly it can happen if you say so, but how does such a thing occur? Could it be that the pilot while experiencing engine failure made a counter move that got out of hand and cut of the tail? Is it even possible for the rotors to hit the tail in such a manner? Or would something have had to bend for that to happen?

On the other hand, it looks to me that the tail broke off, when put under pressure from below (i.e. the ground). Also it looks more like a tear than a break, if it would have broken off there would presumable be more damage around the edge of the break.

The last thing that cought my attention was the place of the break, so I would like to ask the experts. Is it normal for an apache, or any aircraft for that matter to break in the middle of a construction rather than at a mounting point or close to a mounting point? Are aircraft designed to break up in the middle of sections?

(To be clear I'm not an expert by any stretch of the imagination. And my remarks are ofcoarse speculation. But I prefer to speculate rather than waiting for a report, I tend to ask better questions when I'm less informed.)
 

Gremlin29

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I'm looking at the location of the break and the break itself, both are indicative of a blade strike. That section of the tail boom is continuous longerons so it's not going to just break as it has.

The rotors achieve a great amount of rigidity through centrifugal force. When taxiing or during rolling landings you can pull the cyclic full aft without fear of hitting the tailboom. If rotor RPM is low, the blades can definately flex downward enough during a vertical impact to strike the tail which is what I'm guessing happened here. The vertical descent doesn't look like it was that noteworthy since the landing gear are not collapsed (stroked), which they are designed to do in a high impact.

So my guesstimate is they somehow got into a situation that resulted in low main rotor RPM.
 

OPSSG

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Channelnewsasia said:
Apache landing due to corroded valve

By Mustafa Shafawi | Posted: 18 October 2010 1509 hrs

SINGAPORE: Deputy Prime Minister and Defence Minister Teo Chee Hean said investigations showed that a defective component in an Apache helicopter was the cause for an emergency landing last month. The defective component led to the loss of power and shut-down of both engines during flight, forcing pilots to make an emergency landing in an open field in Woodlands. Speaking in Parliament, Mr Teo said the defective component was the Anti-Ice Start Bleed Valve (AISBV).

The AISBV in both engines were found internally corroded when opened up by the manufacturer. The defect was caused by corrosion in the valve which occurred over time. The investigation then focused on why the AISBV was corroded.

Mr Teo said there was no evidence that there were manufacturing defects in those valves. The RSAF maintenance crew have also followed the required maintenance procedures specified by the manufacturer for the aircraft, including the AISBV. Prior to this, there were no reported incidents of the same nature.

Currently, there are no stipulated maintenance checks that would allow such internal corrosion in the AISBV to be detected by the maintainers. The Defence Minister said the maintenance procedure does not call for the RSAF to open up the AISBV. This can be done only by the manufacturer. As stipulated by the manufacturer, the AISBV needs to be replaced only after a fault code appears in the aircraft computer during flight, or when running the engine on the ground for tests.

Mr Teo said the maintenance procedures are now being studied with the manufacturers to see if they need to be modified. This is so that corrosion which occurs inside a valve can be prevented, detected and corrected should it occur.

To ensure the helicopters are fitted only with valves that operate properly, Mr Teo said the RSAF will replace all existing valves and the engines tested thoroughly before each helicopter is cleared for flying....
From the news reported, the AISBVs in both engines of the Apache were affected by the corrosion and Singapore's hot and humid climate does present a particular challenge to aircraft maintenance.

Gremlin29 said:
If they experienced non-pilot induced dual engine failure, it's a first for the Apache and I'll be extremely surprised.
So I guess, Gremlin29 will be surprised by the news of a non-pilot induced dual engine failure. Strange shit does happen but thankfully no one was hurt. :D

I hope Gremlin29 will comment further on how corrosion in the AISBV affects the engines such as to lead to a dual engine shut down. And if he could spare the time, explain in broad strokes how to control a helicopter, to make a hard landing, in the event of both engines shutting down during flight. I'm really interested in learning more. Many thanks in advance.
 
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Red

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Interesting finding. I dont think there is another country which operates the Apache in the same kind of climate Singapore has. Expensive repair for the damaged helicopter and replacement of the valves though Im not sure who will foot the bill; boeing or Singapore or both since it is clearly not RSAF's doing.

Singapore's Minister of Defence full reply in Singapore's Parliament;

Reply by Deputy Prime Minister and Minister For Defence to Parliamentary Questions on Emergency Landing of Apache AH-64 Helicopter

Mr Speaker, Sir, may I have your permission to take Er Lee Bee Wah, Mr Michael Palmer, Mr Low Thia Khiang and Associate Professor Paulin Tay's questions together.

MINDEF has carried out investigations with the aircraft and engine manufacturers into the cause of the loss of power in both engines which led to the incident of the Apache landing in an open field. Following the incident, both engines were sent to the manufacturers for full tear-down and inspection. The manufacturers have identified a defective component which is present in both engines of the aircraft, which led to the loss of power and shut-down of both engines during flight.

The defective component is called the Anti-Ice Start Bleed Valve or AISBV for short. A corroded valve would lead to malfunctioning of the guide vanes that channel air to the aircraft engine. The disruption of airflow to the engine would lead to the loss of engine power. The Anti-Ice Start Bleed Valve (AISBV) in both engines was found internally corroded when opened up by the manufacturer. The defect was caused by corrosion in the valve which occurred over time. The investigation then looked into why the AISBV was corroded and why the corrosion went undetected. We looked into whether there was a manufacturing defect or a maintenance error. Sir, the valves used in the RSAF Apache fleet are the same as those used by other Apache operators around the world. We have no evidence that there were manufacturing defects in these valves. We have also ascertained that the RSAF maintenance crews adhered to the required maintenance procedures specified by the manufacturer for the aircraft, including the AISBV. Prior to this, there were no reported incidents of the same nature. Currently, there are no stipulated maintenance checks that would allow such internal corrosion in the AISBV to be detected by the maintainers. The maintenance procedure does not call for the RSAF to open up the AISBV. This can be done only by the manufacturer. The aircraft operator, in our case the RSAF, needs to replace the AISBV only after a fault code appears in the aircraft computer during flight, or when running the engine on the ground for tests. The nature of the malfunction arising from the corrosion was not detected by the aircraft computer and therefore no fault code was generated. We are now studying, together with aircraft manufacturer, the maintenance procedures to see whether the maintenance procedures mandated by the manufacturer need to be modified so that corrosion which occurs inside this valve is prevented, or can be detected and corrected should it occur.

To ensure that our helicopters are fitted only with valves that operate properly, the RSAF will replace all existing valves with new ones, or valves that are re-certified by the manufacturer, and test the engines thoroughly before we clear each helicopter for flying. Having also reviewed and established that the RSAF's maintenance, flight and training safety procedures are sound, the Apache and the SeaHawk helicopters will progressively resume flying this week.

Mr Speaker, Sir, the RSAF maintains the highest standards of maintenance and flight safety. Let me now turn from the cause of the power loss in the engines, to how the RSAF's pilots are trained to handle emergencies. Training in emergencies is a key part of the training of all our pilots. In the event of an emergency, where possible, the aircraft will be flown back to the nearest airbase immediately. If this is not feasible, the pilots will attempt a safe landing at the nearest open space. In doing so, the key priority is always to avoid populated areas. Safety to the populace has the highest priority and this is what the two pilots did in this incident. When they determined that they were not able to land at an airbase, they considered their options, and found an open space away from buildings and populated areas, verified and confirmed that the field was clear of people, and then executed an emergency landing.

Any unused open plots of land or open fields are potential emergency landing sites for helicopters. Depending on the flight route of the helicopter, various open spaces are identified and briefed as part of the pre-flight procedures for that flight. This is carried out for all RSAF helicopter flights. Hence, it is not possible to identify any specific open spaces as designated emergency landing sites, as emergency landing sites depend on the flight routes being taken and where the emergency occurs. Our pilots are trained to ensure the safety of the public before making a decision to land in any of these open spaces, and they will forego such a landing even at risk to themselves if there is a danger to population.

Let me now turn to the issue of flight training in Singapore and the safety of our population. Mr Speaker, Sir, Singapore is densely populated and has limited airspace. The RSAF also has to share the tight airspace with civilian aircraft. Given these constraints, in addition to local training, the RSAF conducts training in overseas training areas as well as on simulators. The RSAF strikes an appropriate balance amongst these three forms of training. Local training is essential to maintain the proficiency of our Singapore based aircrew, and to ensure that all our pilots are familiar with the local operating environment. Overseas training is more costly but it helps address the airspace constraints our pilots face at home. Simulator training is a useful and effective component of pilot training to improve piloting and operational skills. It allows pilots of varying experience to be trained on aircraft handling under different operational scenarios, and this includes, in particular, training all our pilots on handling the various types of aircraft emergencies.

Mr Speaker, Sir, the safety of our populace is a top priority of MINDEF and the RSAF. We have thus taken steps to ensure that training flights over residential areas are minimised whenever possible, that they are conducted safely, and that they are in accordance to norms prescribed by international aviation bodies, such as the International Civil Aviation Organisation and the Federal Aviation Authority of the United States. These norms govern the minimum flying altitudes designed to ensure the safety of residents living in close proximity to airbases or airports or air fields. They are similar to those adopted in airports which operate in densely-populated cities, as well as where civilian helicopters are used for transportation in major cities and land on helipads on high-rise buildings in densely populated areas. So it is not uncommon for aircraft or helicopters, even civilian ones, to operate over densely populated areas.

While we cannot totally prevent machine failures from occurring, we will do our best to minimise the risk of such failures. The RSAF has in place a comprehensive maintenance programme to ensure the air worthiness of our aircraft. In addition, all our pilots undergo regular emergency aircraft training; and discussions on emergency procedures are carried out as part of every pre-flight preparation. This is to ensure that the pilots are able to respond quickly and professionally in order to minimise any risk posed to the public in the event of an aircraft emergency.
 

Gremlin29

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This is a curious situation and I will be careful here. The AISBV 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.
 

OPSSG

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First of all many, many thanks for taking the trouble to reply.

This is a curious situation and I will be careful here. The AISBV will not cause an engine to shutdown.
I hope I can see what you are driving at. If you don't mind, I'll respond so that you can help me understand your post.

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.
Are you are saying that it could still be a potentially operator or pilot induced issue to an initial mechanical problem?

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.
If I understand you correctly, this is a community of practice issue with maintenance. Meaning that the RSAF's maintenance practices could be further improved. Given that there is only one Apache squadron in Singapore, there's no other in-country expertise to benchmark against. And again, the RSAF will have to look to learning or even re-learning either from US Army Aviation and/or Boeing to improve the existing community of practice in Singapore, in a more proactive manner.

And this is one of the reasons why the RSAF is so keen to learn from the US Military, given the wider base of knowledge and expertise. This is a source of American competitively advantage, during platform selection.

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).
So you are saying that the pilots can potentially recover from AISBV failures? And that it can be potentially mitigated by prompt pilot action, if they took appropriate action. But it did not occur in this Singapore case.

Could you explain what powers the movement of the AISBV? I assume that the value moves due to operator input. Is the valve moment enabled by an actuator (or other such device)? Of does it move because of engine hydraulics (or other such source)?
--> Note that I'm just taking a wild stab in the dark here. Please correct me.

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.
Thanks once again for dealing with my layman questions that may not make sense. :D
 
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Gremlin29

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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.

I have alot of respect for anyone that operates the Longbow, it is the most complex tactical aircraft in the world to fly. I'm not going to say this was a maintenance issue, just that internal corrosion is possible and not unheard of.

I'm not saying Singapore has maintenance issues or that the pilots responded incorrectly because I don't believe we are getting the full facts of the mishap.
 
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