Ainsworth's assurance over "safe" Nimrod
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TD.
As a result of the XV249 incident, when there was evidence of a small fire on the "isolated" cross-feed pipe, two UTI's were issued in order to deterime the temp of the duct during engine start. With the aid of a simple thermocouple and a meter display, the aim was to check the serviceabilty of the shut of valves and determine the residual temperture after starting the engines on the ground. One section, dealing with remedial work states:
"Where temperatures of cross feed ducting recorded during engine ground runs exceeds 200C, both port and starboard cross feed valve and actuator assemblies are to be removed and replaced"
So it has to be assumed that it is IPT's belief that with the cross-feed selected "closed", a defective valve could result in a duct temp in excess of 200C. Although the UTI was carried out some time ago, an official report has yet to be produce. QinitiQ comment on this in their report.
I do not see what all the fuss is about in fitting this monitoring device. In the XV249 report, a guard was recommended for the selector switch. This was rejected because checks are in place, and people do not make mistakes. Now QinetiQ are saying fit a sensor because the temp of the cross-feed duct is unknown for some conditions, this is rejected, because it is believed, by none specialist, that the duct temp will never get near auto-ignition.
Lets think of the plus side of this recommendation. We would take care of the possible inadvertent selection of the cross-feed switch, highlighted in the XV249 report. If the switch was left in the wrong position the Flt Eng would see the temp rise, and question it. A defective cross feed valve would be brought to the attention on the aircrew and necessary action taken. And finally, energency engine starts in air (and they do exist) could be carried out with the Eng monitoring duct temp.
I really can not understand why crews appear to be opposed to a mod which improves flight safety, significantly.
DV
As a result of the XV249 incident, when there was evidence of a small fire on the "isolated" cross-feed pipe, two UTI's were issued in order to deterime the temp of the duct during engine start. With the aid of a simple thermocouple and a meter display, the aim was to check the serviceabilty of the shut of valves and determine the residual temperture after starting the engines on the ground. One section, dealing with remedial work states:
"Where temperatures of cross feed ducting recorded during engine ground runs exceeds 200C, both port and starboard cross feed valve and actuator assemblies are to be removed and replaced"
So it has to be assumed that it is IPT's belief that with the cross-feed selected "closed", a defective valve could result in a duct temp in excess of 200C. Although the UTI was carried out some time ago, an official report has yet to be produce. QinitiQ comment on this in their report.
I do not see what all the fuss is about in fitting this monitoring device. In the XV249 report, a guard was recommended for the selector switch. This was rejected because checks are in place, and people do not make mistakes. Now QinetiQ are saying fit a sensor because the temp of the cross-feed duct is unknown for some conditions, this is rejected, because it is believed, by none specialist, that the duct temp will never get near auto-ignition.
Lets think of the plus side of this recommendation. We would take care of the possible inadvertent selection of the cross-feed switch, highlighted in the XV249 report. If the switch was left in the wrong position the Flt Eng would see the temp rise, and question it. A defective cross feed valve would be brought to the attention on the aircrew and necessary action taken. And finally, energency engine starts in air (and they do exist) could be carried out with the Eng monitoring duct temp.
I really can not understand why crews appear to be opposed to a mod which improves flight safety, significantly.
DV
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DV,
Have you seen where the Start Master Switch is? It is extremely unlikely that this switch could be inadvertantly used to open the cross-feed air supply whilst in flight: especially as engines are no longer routinely shut down. The cross-feed air supply is closed after successful engine start and is to remain closed - a 'red line' limitation in the F700.
Duncs
Have you seen where the Start Master Switch is? It is extremely unlikely that this switch could be inadvertantly used to open the cross-feed air supply whilst in flight: especially as engines are no longer routinely shut down. The cross-feed air supply is closed after successful engine start and is to remain closed - a 'red line' limitation in the F700.
Duncs
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DDS:
Yes, and I am looking at it right now. According to the Human Factors Report, associated with the XV249 investigation, the probability of inadvertent operation (being left open after engine start, or being knocked in flight) was set at "probable" (Will occur several times in life of item). A red line entry does not guarantee anything.
This is not my judgement, it is the judgement of the RAF Centre of Aviation Medicine.
DV
Have you seen where the Start Master Switch is?
This is not my judgement, it is the judgement of the RAF Centre of Aviation Medicine.
DV
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DV,
There is no hard guarantee that the crossfeed valves will remain closed in every future flight, due to human factors. Somebody will probably make a mistake one day. But, on that exact same flight when the mistake occurs, there has to be a fuel leak onto the crossfeed pipe for that mistake to be serious. This would have to be a new fuel leak, that starts during that flight, because the maintenance schedules require 100% examination of all fuel pipe couplings in the bomb bay and rear pannier before and after every flight.
Flight safety is definitely not compromised by not guarding the switch.
Incidentally, the only possible mistake that could be made in flight is to leave the switch at AIR ASSIST after ground starts, and a guard will not stop that mistake. The switch incorporates a positive action mechanism, which means that it cannot be accidentally brushed from one position to the other. It is effectively self-guarding against accidental operation. The officer who recommended the mod is a ground engineer because the incident with XV249 occured during ground maintenance. Had he been a flight engineer (and I'm not suggesting that the investigating offcer shoud have been an FE), I know that the thought of guarding the switch would not have entered his mind.
If the groundcrew want to protect the switch during engine runs, thats their business, not mine. I know that they start and stop the engines more than once during the runs and if they have an agreed opinion that proposes a guard, then they should start the process. However, they have a solid checklist that prevents the switch from being left open, so I would be very surprised if they want the guard.
Finally, that incident gave rise to RPM limits during engine ground starts to ensure that whenever the crossfeed pipe is open it cannot get hot enough to ignite any fluid (that should not be there anyway). This is a sensible precaution because it mitigates against a single failure during normal operation. The single failure being a fluid leak onto a hot crossfeed pipe during engine ground starts.
Ed Sett
There is no hard guarantee that the crossfeed valves will remain closed in every future flight, due to human factors. Somebody will probably make a mistake one day. But, on that exact same flight when the mistake occurs, there has to be a fuel leak onto the crossfeed pipe for that mistake to be serious. This would have to be a new fuel leak, that starts during that flight, because the maintenance schedules require 100% examination of all fuel pipe couplings in the bomb bay and rear pannier before and after every flight.
Flight safety is definitely not compromised by not guarding the switch.
Incidentally, the only possible mistake that could be made in flight is to leave the switch at AIR ASSIST after ground starts, and a guard will not stop that mistake. The switch incorporates a positive action mechanism, which means that it cannot be accidentally brushed from one position to the other. It is effectively self-guarding against accidental operation. The officer who recommended the mod is a ground engineer because the incident with XV249 occured during ground maintenance. Had he been a flight engineer (and I'm not suggesting that the investigating offcer shoud have been an FE), I know that the thought of guarding the switch would not have entered his mind.
If the groundcrew want to protect the switch during engine runs, thats their business, not mine. I know that they start and stop the engines more than once during the runs and if they have an agreed opinion that proposes a guard, then they should start the process. However, they have a solid checklist that prevents the switch from being left open, so I would be very surprised if they want the guard.
Finally, that incident gave rise to RPM limits during engine ground starts to ensure that whenever the crossfeed pipe is open it cannot get hot enough to ignite any fluid (that should not be there anyway). This is a sensible precaution because it mitigates against a single failure during normal operation. The single failure being a fluid leak onto a hot crossfeed pipe during engine ground starts.
Ed Sett
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EdSett100;
At post #48 you stated:
"I am aware that QQ suggested a gauge in their report, because the individual they spoke to about this aspect of their investigation was a flight engineer. He also added that, as an eng, he is interested in everything that can happen in the aircraft and that it would be useful to know if a closed valve had leakage, so that he could report it when he landed. Thats all very well, for the purpose of monitoring one system, but there has to be additional failures before that defect contributes to a fire leading to a crash. We do not mitigate against double or triple failures. We will not use up resources just to provide the air engineer with another "useful" gauge look at. "
Then at post #67
"The officer who recommended the mod is a ground engineer because the incident with XV249 occured during ground maintenance. Had he been a flight engineer (and I'm not suggesting that the investigating offcer shoud have been an FE), I know that the thought of guarding the switch would not have entered his mind"
In the first case you seem to reject the idea, because it is a Flt Eng's view, and then you reject the second suggestion because it came from a ground engineer. What type of engineer do you accept? Surely fitting a sensor would satisfy both and improve flight safety. You are not mitigating against a "double" failure, but a "single" fuel leak onto a high temp cross-feed pipe caused by a pre-existing shut off valve defect. This defect would not be detected by any pre or post flight inspection.
To accept additional monitoring, is not a sign of unprofessionalism, or going soft, it is common sense. Just to remind you that airworthiness is defined as the ability of an aircraft to operate without significant hazard to aircrew, or to the general public over which it is flown.
DV
At post #48 you stated:
"I am aware that QQ suggested a gauge in their report, because the individual they spoke to about this aspect of their investigation was a flight engineer. He also added that, as an eng, he is interested in everything that can happen in the aircraft and that it would be useful to know if a closed valve had leakage, so that he could report it when he landed. Thats all very well, for the purpose of monitoring one system, but there has to be additional failures before that defect contributes to a fire leading to a crash. We do not mitigate against double or triple failures. We will not use up resources just to provide the air engineer with another "useful" gauge look at. "
Then at post #67
"The officer who recommended the mod is a ground engineer because the incident with XV249 occured during ground maintenance. Had he been a flight engineer (and I'm not suggesting that the investigating offcer shoud have been an FE), I know that the thought of guarding the switch would not have entered his mind"
In the first case you seem to reject the idea, because it is a Flt Eng's view, and then you reject the second suggestion because it came from a ground engineer. What type of engineer do you accept? Surely fitting a sensor would satisfy both and improve flight safety. You are not mitigating against a "double" failure, but a "single" fuel leak onto a high temp cross-feed pipe caused by a pre-existing shut off valve defect. This defect would not be detected by any pre or post flight inspection.
To accept additional monitoring, is not a sign of unprofessionalism, or going soft, it is common sense. Just to remind you that airworthiness is defined as the ability of an aircraft to operate without significant hazard to aircrew, or to the general public over which it is flown.
DV
Last edited by Distant Voice; 29th Jun 2009 at 14:18.
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DV,
Thanks for pointing me in the direction of the XV249 Human Factors Report. Personally, I am not convinced that a Nimrod pilot could PROBABLY inadvertantly select AIR ASSIST; although, I admit that the after start checks do not require confirmation the the MIs are SHUT; only that the start selector has been selected to WINDMILL. However, after engine start, there is no reason to have your hands anywhere near the Start Master Switch - the switches next to it are for alternative start procedures. However, as you rightly stated, the judgement of CAM was that it was PROBABLE.
Duncs
Thanks for pointing me in the direction of the XV249 Human Factors Report. Personally, I am not convinced that a Nimrod pilot could PROBABLY inadvertantly select AIR ASSIST; although, I admit that the after start checks do not require confirmation the the MIs are SHUT; only that the start selector has been selected to WINDMILL. However, after engine start, there is no reason to have your hands anywhere near the Start Master Switch - the switches next to it are for alternative start procedures. However, as you rightly stated, the judgement of CAM was that it was PROBABLE.
Duncs
