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logic28

Undetected Warning Sound

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Hello everybody,


 


Being away from home and my P3D for a few months I have to make do with my Macbook Pro in Windows mode running FSX for my ATIS communication training before I enter the Vatsim world.


 


Ever since yesterday tough, flying from EHRD to LOWI I have been getting this warning sound no matter what I do.


It seems to be related to either the time lapsed from the beginning of the flight or indeed the altitude (normally above FL 200)


All faults have been reseted in the CDU but every time I restart the flight  and  look in the Aircraft section of the CDU, I find that the brakes fault is active again.


Don’t now if this is triggering the warning though.


 


I appreciate your help so please leave a comment if you  think you know what this might be.


Thanks


 


 



 


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Wow .... well spotted ! .... its supposed to be taken care of by the FS2Crew but recently he his forgetting a few things like Engine switches .... Lights and so on ......


 


Thanks for that.... however it’s strange that the prssur.  gage was showing normal readings and Iv'e  just noticed that the altitude horn cut off stops the warning ..... so obviously the pressurisation must be obtained by the bleed air though the Air Con..... 


 


 


Cheers 

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your  correct its  supposed  to be taken  by your  FO   maybe  it  was  his  day off:)  maybe  you can post your  issue  at the fscrew  forum   maybe Bryan  would  know  your  issue  could  be  just  specific to your  set  up

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You provided a wonderful example of why the cabin altitude and takeoff config lights were added.  It can be confusing without any sort of visual indication what’s going on especially considering in the real situation cognitive skills would be starting to degrade due to the onset of hypoxia.

 

If you look closely at your cabin altitude (small pointer) you’ll see it’s above 10,000’.

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You provided a wonderful example of why the cabin altitude and takeoff config lights were added.  It can be confusing without any sort of visual indication what’s going on especially considering in the real situation cognitive skills would be starting to degrade due to the onset of hypoxia.

 

If you look closely at your cabin altitude (small pointer) you’ll see it’s above 10,000’.

 

I am not familiar with the implementation of such lights..... are we now talking about the real aircraft or the PMDG?

At home, (I am away at the moment hence the laptop on FSX) I have the P3D laters version of the PMDG; am I likely to find those lights tin that cockpit by any chance?

Or is this something that has been introduced only on later models of aircraft?

 

Its funny how a simple domestic simulator can give very serious indications about real potential tragic events, thumbs up for PMDG.

 

Having said so there are some functionalities yet not incorporated in the 738NG that might come useful if aiming to a full training such as the LGC (long range cruise option) int the cruise page of the CDU.   

 

your  correct its  supposed  to be taken  by your  FO   maybe  it  was  his  day off:)  maybe  you can post your  issue  at the fscrew  forum   maybe Bryan  would  know  your  issue  could  be  just  specific to your  set  up

Yes maybe I will but first I need to reproduce the problem at least a couple of times. Also FS2Crew has been behaving rather strangely recently on this setup (Different from my P3D at home).

It seems to jump procedures and in some cases it doe not progress through the stages and needs nudging manually (that's when hi most probably forgets things).

 have known my FO to configure the plane for takeoff and forget turn the engine switches to continuos as well as the probe heat etc...

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This is what the real later-model aircraft looks like:

cabinaltitudelights.jpg

 

The NGX models an earlier model.

 

Full names - first and last - in the forum, please.

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You provided a wonderful example of why the cabin altitude and takeoff config lights were added.  It can be confusing without any sort of visual indication what’s going on especially considering in the real situation cognitive skills would be starting to degrade due to the onset of hypoxia.

 

If you look closely at your cabin altitude (small pointer) you’ll see it’s above 10,000’.

The lights were added to differentiate between the two possible causes of the intermittent horn. Yet it wasn't confusing for about 30 years. In the 1960s, when the 737 first flew, the crew were expected to know the various aural warning sounds and what they meant. The intermittent horn is the only one which has two meanings, but if it sounds in flight it can only mean one thing, excessive cabin altitude. The 737 is something of a throwback in terms of its caution alerting system. More modern aircraft use aural alerts to tell the crew to look at EICAS/ECAM and identify the problem. The 737 has a mixture of caution lights (with no aural) and aural warnings (with no lights) and no EICAS. The 707, 727 and 747-200 were very similar in that respect.

 

At 10,000 ft hypoxia should not be a significant problem. The intermittent horn should direct the crew to look at the pressurisation panel and nowhere else. In the Helios accident that's exactly what the crew did, but the bleeds and packs were switched on so it seemed the pressurisation was properly set.

 

 

however it’s strange that the prssur. gage was showing normal readings and Iv'e just noticed that the altitude horn cut off stops the warning

 

But the cabin pressure gauge was not showing normal readings. However the abnormality isn't that obvious, there's no marking on the cabin altitude scale to show where the safe limit is. It's quite likely the Helios 737 crew made the same mistake and didn't spot the abnormal cabin altitude. The horn cutoff is designed to work like that, by the way. Once cancelled the horn will not restart whatever the cabin altitude is. The idea is that the crew can cancel the deafening sound while they work to reset the system.

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The lights were added to differentiate between the two possible causes of the intermittent horn. Yet it wasn't confusing for about 30 years. In the 1960s, when the 737 first flew, the crew were expected to know the various aural warning sounds and what they meant.

Pilots are still supposed to know what the horn means today but that doesn’t mean we shouldn’t make the systems safer when we can. Your Helios example proves that, they looked at the pressurization and it looked normal so they assumed the takeoff configuration warning was malfunctioning.

 

At 10,000 ft hypoxia should not be a significant problem.

Even at 10000’ your blood saturation level is already low enough to impair judgment and vision. Euphoria also sets in which further delays the recognition you have a problem.

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Well, it turned out to be a very interesting and educational conversation, so thank you all for your inputs.

 

Meanwhile I went back to my books and discovered many details that I seemed to have overlooked, maybe due to the excitement of getting into the cockpit and fly.

 

Now, having covered the basics well,  I am reviewing all my courses and squeezing any additional information that slipped out previously.

 

Thank you all

 

Regards

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Pilots are still supposed to know what the horn means today but that doesn’t mean we shouldn’t make the systems safer when we can. Your Helios example proves that, they looked at the pressurization and it looked normal so they assumed the takeoff configuration warning was malfunctioning.

 

 

Even at 10000’ your blood saturation level is already low enough to impair judgment and vision. Euphoria also sets in which further delays the recognition you have a problem.

What the Helios example shows is that the crew didn't check the pressurisation properly. They didn't check cabin altitude (obvious to look at you would have thought), nor outflow valve position. If they had pressed the horn cutoff it would have silenced the horn and proved it was nothing to do with takeoff configuration. Most importantly they hadn't checked the pressurisation was in AUTO during preflight (it had been left in CHECK mode). It was illogical to think the TO config warning could malfunction in flight without a thorough check of what the aural alert was really telling them.

 

I can't say I've noticed either impaired vision or judgement at 10,000 feet. Mild breathlessness during exertion yes. I doubt any such impairment was significant initially. Of course as the fault finding went on the altitude increased and the decision making would have got worse as a result. The initial reaction should have been sort the pressurisation out. Just as the initial reaction to a fire bell is to do the fire procedure, not wonder if the warning system is malfunctioning.

 

The system was already safe. Adding the additional warning lights was a belt and braces action to make sure no one can repeat the error, despite their training. However a much better idea would have been to upgrade the caution and warning system in the 737 to modern standards when the 737NG was designed in the first place. The 737MAX will retain the same outmoded system too.

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Even at 10000’ your blood saturation level is already low enough to impair judgment and vision. Euphoria also sets in which further delays the recognition you have a problem.

 

Maybe for some, but Denver residents will probably not notice.  I used to fly frequently at 12500 before I moved to a pressurized aircraft, and cabin altitudes of 8000 are routine in part 25 operations. I've lost pressurization twice, so far, and first time at FL230, it's not too bad below 19000 but of course I kept heading lower to 12000 to comply with FAR 91. Second time it was during climb and I noticed at 14000.  Granted, the USAF has a night time limit of 10000 but that is being conservative.

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I did two hour flights at 12,000 IFR and below VFR for quite a while with no problems, but I was 30 years younger. I remember back in 1999 at La Paz Bolivia when I went outside the airport at 13,800 feet I started to feel really bad. It had a long lasting effect. I guess this varies with the individual and age and physical fitness ?

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Of course my statement wasn’t intended to imply that conducting a safe flight with a cabin altitude at or above 10000’ wasn’t possible.  I too have flown several flights above 10000’ without O2.  I intended to indicate that at 10000’ your blood saturation level is already below the level deemed necessary for 100% normal functioning.  Yes it impacts everyone differently, and those that live at higher altitudes will have a better tolerance up to a certain point.  The rate at which the altitude change occurs can also have an effect, the faster the change the harder it is for your body to adjust. 
My statement was also directly in relation to this context which is a 737 in a climb and usually well above 10000’ when the cabin altitude warning goes off.  This means the cabin is still climbing to match the aircraft altitude, and with every passing moment the cabin altitude is getting higher.  The first response should always O2 masks on and a descent, then any further troubleshooting as required.  A search of the ASRS database also reveals that the confusion of the horn prior to the addition of the lights is not unique to the Helios flight.  
 
There’s a good article on hypoxia here:
http://www.flightsafetyaustralia.com/2014/08/do-not-go-gentle-the-harsh-facts-of-hypoxia/

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and with every passing moment the cabin altitude is getting higher. The first response should always O2 masks on and a descent, then any further troubleshooting as required.

 

Agree 100%

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I intended to indicate that at 10000’ your blood saturation level is already below the level deemed necessary for 100% normal functioning. Yes it impacts everyone differently, and those that live at higher altitudes will have a better tolerance up to a certain point.

 

I don't doubt the physiological evidence, or that the level is below 100% functioning, just the amount it affects people. Below normal funcitoning is not a binary situation. Functioning at 10,000 ft will be better than at 14,000 ft for example. BTW, I'm by no means accustomed to 10,000 ft altitude, but when I have experienced it I didn't notice any significant effect. I realise it's subjective and I may have over-estimated my ability. However I would suggest that at 10,000 ft cabin the crew should have still been physically capable of taking the correct action. The unlikely assumption that it was a TO config warning was a terrible distraction which lead to delay in dealing with the real problem. By that time the cabin altitude would have been much higher than 10,000 ft and decision making would have become progressively more difficult.

 

Training should kick in when an aural warning like this occurs. I'm well aware there were previous instances of such confusion, but no competent 737 crew (or 707, 727 and 747 Classic crew for that matter) should ever be confused as to the cause of the intermittent horn going off in flight. The additional lights aren't necessary, but they do add to situational awareness and will prevent another crew making such a basic mistake. They haven't been mandated in the 747-200 for example, yet the problem there is exactly the same.

 

 

My statement was also directly in relation to this context which is a 737 in a climb and usually well above 10000’ when the cabin altitude warning goes off.

 

With respect, the aircraft altitude that the horn goes off at is irrelevant. The relevant altitude, in terms of oxygen levels, is that of the cabin. That was the altitude I meant throughout.

 

 

The first response should always O2 masks on and a descent, then any further troubleshooting as required.

Agree 100%

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