B737 Classic Pack Trip Off Nnc

[LEM]

.....
If both PACK TRIP OFF lights remain illuminated:

DESCENT....................................ACCOMPLISH

At level off:



AIRSPEED.....................................290 KNOTS MINIMUM



Can anyone on earth explain why at lower speeds "Flight deck and cabin temperatures may increase rapidly"?


Thanks

[alexban]

HY LEM

I'm a bit tired now,but it's an interesting question.The only answer that I think of is that by increasing speed you'll increase the ventilation in the plane. As you see in the NNC the temperature will increase due to instruments,lighting,entertainment systems ,galley...You should depressurize the plane selecting outflow valve full open to increase airplane ventilation.I think the speed helps here.
The flow control valve will also open to help cooling the E&E bay.
Initially I thought about the ram air,but the packs are off,so this doesn't matter anymore,the packs valves are closed-no air through the packs.
Brgds
Alex

[LEM]

Hy alex, unfortunately this is no Falcon or Bac111, since no air is coming out of the packs anymore, I really don't see how we can ventilate the airplane!


Hmmm... let me think...

Assuming the shape of the fuselage creates a depression around it because of increased airflow velocity (Bernoulli), some warm air can be sucked out of the airplane through various outflow valves, but how is fresh air entering the airplane????

[woderick]

my fading memory recalls a ram air valve ?

[DDG]

Rapid increases in heat would be due to the lack of cool conditioned air being supplied to the flight deck as the flight deck area recieves conditioned air from the LH pack (as opposed to conditioned air & recirculated air for the cabin) which assists in equipment cooling(remember ther is a large amount of electronic equipment in the cockpit that require cooling).
Also by nature the flight deck will suffer from solar heating as there is a large amount of window area in the flight deck.
The flight deck will not benefit from any real "draughts" from the Fwd outflow valve (if fitted) as it is connected to the equipment cooling exhaust and is controlled by the recirculation fan switch position and aft outflow valve position.The equipment cooling valve outlet will have been closed until cabin differential pressure can be reduced to 2.5psi (this will cause a rapid rise in cockpit temps),once achieved this will be the major outlet for the forward cabin to atmosphere and will provide some ventilitation.

Regards DDG

[alexban]

LEM hy
I thinkyou figured it right: the speed will create ,probably ,a suction effect,and remember also that there are more than one valves open now.Also the negative pressure relieve valves.So ,probably,due to aerodinamics,and shape of fuselage,the air will be sucked out through
some of the valves (ex forward outflow,or flow control valve ) and because of the depression in the fuselage will enter through other openings (ex main outflow valve)Position of the valves differ,maybe the suction effect will differ.
This must be the answer,I guess
Alex

[LEM]

Yeah, that's probably the only answer...

The last thing to try would be opening the side windows, and I wonder what would be the effect, apart from the awful noise...