Jump to content

Archived

This topic is now archived and is closed to further replies.

Aexeron

A question regarding Pressurization

Recommended Posts

I have recently experienced a problem with the 737NGX pressurization system, entirely my fault: The Pressurization Mode Selector (ironically, PMS) on the Digital Cabin Pressure Control System (DCPCS) was set to Manual. On my initial overhead scan, I completely missed the "MANUAL" light (perhaps because it was green), and continued on. About 3500 meters up, I encountered what sounded like the takeoff configuration aural warning, obviously sparking some confusion. About 5000 up, and the Master Caution appeared, along with "AIR COND" on the Flight Director's recall. Initially, I thought something was wrong with just that -- the air conditioning. I tried tweaking a few knobs, but nothing seemed to work. Then, I looked up at the upper overhead and saw "PASS OXY ON." Uh oh. It clicked then, I had a pressurization error! I had not even thought of it due to the similarities between the Takeoff Configuration aural warning and the Pressurization aural warnings.

 

Since then, I have done a bit more research on the pressurization system in 737s, and noticed a very similar incident to mine: Helios 522. Following that incident, Boeing added a "CABIN ALTITUDE" warning on panels P1 and P3 of the 737, as shown:

 

cabinaltitudelights.jpg

 

My question is: Why doesn't the PMDG 737NGX have these lights? Shown below is the current configuration of panel P3:

74777095.png

 

 

Is there the possibility of these lights being added to clarify an already bad situation?


Ian A. Zimmérman

Button pusher extraordinaire

Share this post


Link to post
Share on other sites

The real aircraft NGX is modelled after did not have this mod, thus the NGX does not have this mod. AFAIK there are no plans to add it, at this point.


--Peter Fabian 
RTFM.jpg

Share this post


Link to post
Share on other sites

Hi there,

first Helios 522 was a 737-300, not a NG. Then in order not to confuse the pilots too much, aural Warnings are used for different situations, i.e. the "Takeoff" Warning. The sound only means Takeoff warning when you are about to take off. It also sounds for example with flaps 15 or more and gear not extended. You as a (typerated) pilot should what the bell means at what time. Under heavy workload you wouldnt be able (or at least the most of us) top distinguish between different rhythm to identify a problem. This is why same some is used in different Phases of flight. But: This does not explain, why they (Boeing) took the light away.. it helps for clarification but again one more light that flashes and might draw your attention from something more important... cheers

Share this post


Link to post
Share on other sites

They didn't take the light away... They added it.


Name available upon request


AVSIMSig.jpg


 

Share this post


Link to post
Share on other sites

The TOCW horn going off in mid flight is clearly something unusual (because one has already taken-off!) Which is why it is usually reserved for cabin height being above 10,000ft. It is usually a very loud attention getting warning. The cabin altitude can be a result of a slow leakage or sudden depressurisation. In either case stick the masks on. Depending on a/c type oxygen is released into the cabin ring main manually or automatically which is conditional on cabin altitude. Unless the a/c is equiped with chemical cannisters (which are a one time only use and last a few minutes).


3VlzBGn.jpg?1

Super VC10 into LOWI with PF3 at a cinema near you

https://www.youtube.com/watch?v=298UDyNmgUA

 

Share this post


Link to post
Share on other sites

The TOCW horn going off in mid flight is clearly something unusual (because one has already taken-off!) Which is why it is usually reserved for cabin height being above 10,000ft. It is usually a very loud attention getting warning. The cabin altitude can be a result of a slow leakage or sudden depressurisation. In either case stick the masks on. Depending on a/c type oxygen is released into the cabin ring main manually or automatically which is conditional on cabin altitude. Unless the a/c is equiped with chemical cannisters (which are a one time only use and last a few minutes).

 

In the case of Helios 522, the cockpit oxygen masks did not automatically deploy, so the pilots had no indication of pressurization problems. Given that the takeoff config aural warning and the pressurization aural warning is the same tone, a pilot would think that the takeoff config warning was on the fritz, mainly because pressurization warnings are very far and few between. This is supported by contact between Helios 522 and Helios engineering department -- "Where is the takeoff config circuit breaker?"

 

Boeing added these lights to allow pilots to differentiate between two very similar warning tones. It shouldn't be too hard to implement on the NGX in future service packs.


Ian A. Zimmérman

Button pusher extraordinaire

Share this post


Link to post
Share on other sites

I never understood why Boeing never decided to simply make the CA>10K warning an aural alert similar to the GPWS warnings. Right now if you are flying towards a mountain, you don't hear a loud ding, you hear "WHOOP WHOOP - PULL UP!" or "TERRAIN TERRAIN - PULL UP!" telling you just what's wrong. Similarly, if you're cabin altitude climbs above 10,000 feet, it seems to me like Boeing should have added an aural alert similar to "WHOOP WHOOP - CABIN ALTITUDE!" - The fact that they didn't seems to have led a lot of room for confusion amongst crews, in my opinion.


Rules of Wisdom:
Take-offs are optional, landings are mandatory.
The only time you have too much fuel is when you're on fire.
Your airline can only make a small fortune by starting with an even larger fortune.

Share this post


Link to post
Share on other sites

So many easy ways to save lives, so many bucks to change the aircraft certificates, training, etc.

 

The answer is $$$$$$.


Matt Cee

Share this post


Link to post
Share on other sites

In the case of Helios 522, the cockpit oxygen masks did not automatically deploy,

 

They never deploy, the pilots have to manually pull them out of their little storage box and the masks themselves are much different from the passenger masks.

 

http://www.b737.org.uk/emergency_equipment.htm

 

 

Given that the takeoff config aural warning and the pressurization aural warning is the same tone, a pilot would think that the takeoff config warning was on the fritz, mainly because pressurization warnings are very far and few between. This is supported by contact between Helios 522 and Helios engineering department -- "Where is the takeoff config circuit breaker?"

 

That and hypoxia also added to the confusion. According to the Greek investigation the FO had prior issues with not following checklists so I can see how he missed the auto switch during his preflight panel flow.


Alex Jevdic KORD/KHOT/KPWK

A<380 love at first flight

Share this post


Link to post
Share on other sites

That and hypoxia also added to the confusion. According to the Greek investigation the FO had prior issues with not following checklists so I can see how he missed the auto switch during his preflight panel flow.

 

Confusion could be averted by having clearer warnings. Hence why they added the lights to differentiate the two warning types. Pressurization warnings, being so important, should be very clear and understandable.


Ian A. Zimmérman

Button pusher extraordinaire

Share this post


Link to post
Share on other sites

They never deploy, the pilots have to manually pull them out of their little storage box and the masks themselves are much different from the passenger masks.

 

http://www.b737.org....y_equipment.htm

 

 

That and hypoxia also added to the confusion. According to the Greek investigation the FO had prior issues with not following checklists so I can see how he missed the auto switch during his preflight panel flow.

 

 

Perhaps not enough training is/was given. The TOCW horn means such "only" on the ground during the take-off roll or a high speed taxi. If it sounds in the air i.e. once airborne! it isn't the TOCW horn any more its the cabin pressure warning. Obviously to hear the horn at FL350 and "not" during take-off means that the take-off was probably ok or at least 7 out of 10! Also it depends on the type of warning given. Is it a gentle reminder as is the stall warning of the A330 ("Stall-Stall, sotto voce!). Or is it as in the VC10 a very loud intermittent horn (in the real sense!) that most definately gets your attention.

 

As for hypoxia this is why it is imperative that pilots don their masks as soon as the warning is given. Regardless of whether the cabin leak is slow or sudden.


3VlzBGn.jpg?1

Super VC10 into LOWI with PF3 at a cinema near you

https://www.youtube.com/watch?v=298UDyNmgUA

 

Share this post


Link to post
Share on other sites

I never understood why Boeing never decided to simply make the CA>10K warning an aural alert similar to the GPWS warnings. Right now if you are flying towards a mountain, you don't hear a loud ding, you hear "WHOOP WHOOP - PULL UP!" or "TERRAIN TERRAIN - PULL UP!" telling you just what's wrong. Similarly, if you're cabin altitude climbs above 10,000 feet, it seems to me like Boeing should have added an aural alert similar to "WHOOP WHOOP - CABIN ALTITUDE!" - The fact that they didn't seems to have led a lot of room for confusion amongst crews, in my opinion.

 

Because in-built warnings are an essential part of the airplane and as they were built in the sixties, there was not technology to make them speak out the condition. EGPWS is meanwhile a new technology that was glued on to the 737 and is not an integral part of the airframe itself.

 

The issue is then similar to why EICAS was not introduced in the NG - crew training, crew rating and type certification.


--Peter Fabian 
RTFM.jpg

Share this post


Link to post
Share on other sites

the cockpit oxygen masks did not automatically deploy, so the pilots had no indication of pressurization problems.

 

Hi Aexeron,

 

There are no such thing in the cockpit. The oxygen mask are quick donning type.

 

Regards,


Martin Dahlerup

My rig contains a random selection of computer parts working in perfect harmony....

 

I hold a EASA fATPL + A320 SIC rating and a FAA CPL with CFI rating.

Share this post


Link to post
Share on other sites

Because in-built warnings are an essential part of the airplane and as they were built in the sixties, there was not technology to make them speak out the condition. EGPWS is meanwhile a new technology that was glued on to the 737 and is not an integral part of the airframe itself.

 

The issue is then similar to why EICAS was not introduced in the NG - crew training, crew rating and type certification.

 

While true, I always figured they could just foot the bill and integrate more modern updates to the airplane, including but not limited to switching the audio hardware and software and .wav file associated with the horn, and replacing it with newer hard/software and a "WHOOP WHOOP - CABIN ALTITUDE."

 

While I understand it's not nearly as easy as that, the point is that as time progresses, aircraft evolve to meet the demands of the present. The 737 NG is extremely new, and considerations such as new aural alerts and better crew advisories should have been given more thought by Boeing - and perhaps they'll consider it with the 737 NEO.

 

Or maybe they won't.


Rules of Wisdom:
Take-offs are optional, landings are mandatory.
The only time you have too much fuel is when you're on fire.
Your airline can only make a small fortune by starting with an even larger fortune.

Share this post


Link to post
Share on other sites

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    35%
    $8,760.00 of $25,000.00 Donate Now
×
×
  • Create New...