Simviation Forum - A Question

Jul 24^th, 2012 at 9:55pm

U4EA Offline
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For all the experts here:

Say it's about 107 ambient ramp temp and you have a parked 737-300 that's been at the gate since arrival for about 50 minutes.

After shutdown there's either ground power or APU while sitting parked. Unknown which was the provider.

Say, at boarding time, inside cabin temp is easily low to mid 90s. Passengers load, mains start after pushback, and there is absolutely no change in air temp blowing out of the passenger vents which may or may not be significant.

BUT, after take-off and climbout to 28,000 there still is no change in the hot air the vents are blowing!

Now the query for the experts: I realize that ambient air temp at 28,000 should be significantly lower than at ramp elevation. And I realize that the mains are running at capacity therefore providing full power to all systems, like the air-conditioning. So, with that in mind, was the crew possibly not fully versed on maintaining passenger comfort, or was the plane broke.

The side effect was that methinks I lost a good bit of water weight in the 'sauna' I was trapped in. Shocked

Thanx for any responses! Cool

I love the smell of radials in the morning!

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Reply #1 - Jul 24^th, 2012 at 10:17pm

planephysician Offline
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The Temp Controller may have been set to "hot", not working or the Packs may not be on. Was there a sufficient amount of airflow from the gasper? The Recirc Fan may have been the only thing running and it was blowing the same, hot, cabin air that was there when you boarded. Of course, if you were in STL you were a victim of the humidity and the Packs weren't able to cool it enough. Seen that one a number of times!

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Reply #2 - Jul 24^th, 2012 at 10:55pm

U4EA Offline
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That was probably it, and sorta what I suspected. We were at Chicago Midway, destination KSTL, yesterday evening. Air temp at the time was around 95 so I guessed that ambient ramp temp was somwhere in the 102-108 range.

I suppose that the outside air they intaked in-flight loses it's 'coolness' when it's compressed to enhance its 'breathe-ability'?

They probably let the temp get away from 'em, or the A/C system was overloaded, and niether condition was addressable til the sun went down.

Felt bad for the folks that had to stay on at StL for continuance to LAX. Cry

I love the smell of radials in the morning!

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Reply #3 - Jul 25^th, 2012 at 10:03am

expat Offline
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U4EA wrote on Jul 24^th, 2012 at 10:55pm:

That was probably it, and sorta what I suspected. We were at Chicago Midway, destination KSTL, yesterday evening. Air temp at the time was around 95 so I guessed that ambient ramp temp was somwhere in the 102-108 range.

I suppose that the outside air they intaked in-flight loses it's 'coolness' when it's compressed to enhance its 'breathe-ability'?

They probably let the temp get away from 'em, or the A/C system was overloaded, and niether condition was addressable til the sun went down.

Felt bad for the folks that had to stay on at StL for continuance to LAX. Cry

You are both being rather simplistic in you thinking on this problem. Firstly the system would not have been overloaded at any altitude. The pneumatic system produces around 8 times the required air quantity at any given engine speed or altitude. The only time it is turned off is during engine start and then if the ambient temperature is very, very high during the take off run as all cabin air comes from either 5th or 9th stage depending on engine RPM. Don't forget cabin heating or cooling is a secondary effect/function of the air system. The first being cabin pressurisation. Also saying the at crew does not know how to use it properly, a little insulting me thinks..
From what you felt in the cabin, you could not really diagnose the problem. You would have needed to speak to the cockpit crew to ascertain duct temperatures and pressures for the supply lines to the pneumatic system. Not only that, but you would have needed to know altitude and engine RMP too. Also flow quantity from the gaspers in the cabin does not indicate anything.

Below are the system diagrams for the pneumatic systems for the aircraft and the altitude pressure graph. Not so simple is it.....

This graph is from my 737NG notes, but the 737 classic will be similar.

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B1 Boeing 737-800 and Dash8 Q-400

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Reply #4 - Jul 25^th, 2012 at 11:48pm

U4EA Offline
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Thanx Expat! I wasn't trying to be insulting, but if something was broke I would think they would've announced something or had a different response than, "We're trying to do the best we can."

It was either one of three possibles IMHO: a) broke, b) overload, or c) operator malfunction.

A straight answer from the attendants would've been nice, but they could've been gettin' smoke blown up their butts by the drivers and not known any better.

I love the smell of radials in the morning!

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Reply #5 - Jul 29^th, 2012 at 8:03pm

planephysician Offline
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Well, I guess being a 30+ yr mechanic who works on these systems daily doesn't qualify my answer I guess - my bad!

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Reply #6 - Jul 29^th, 2012 at 11:20pm

wahubna Offline
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planephysician wrote on Jul 29^th, 2012 at 8:03pm:

Well, I guess being a 30+ yr mechanic who works on these systems daily doesn't qualify my answer I guess - my bad!

There is always room to learn...so maybe the sarcasm can go.

I have been working on WACOs for a couple of months, but I have managed to learn some things about them that the folks that have been building and maintaining them for 15years did not realize..because I have a different view point.

‎"At that time [1909] the chief engineer was almost always the chief test pilot as well. That had the fortunate result of eliminating poor engineering early in aviation."- Igor Sikorsky

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Reply #7 - Jul 30^th, 2012 at 9:25am

expat Offline
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planephysician wrote on Jul 29^th, 2012 at 8:03pm:

Well, I guess being a 30+ yr mechanic who works on these systems daily doesn't qualify my answer I guess - my bad!

I am 5 years behind you and still learning every day Cheesy

Matt

PS, Why not post that you work in these systems when you gave your answer, saves a lot of time and I would have changed the way I replied and not trodden on your toes

PETA People Eating Tasty Animals.

B1 Boeing 737-800 and Dash8 Q-400

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