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Posted on 7/1/22 at 8:23 pm to TheFlyingTiger
At the gate the A/C is usually either being provided by pre-conditioned air (PCA) an A/C unit attached to the jet bridge with a big yellow hose that feeds air to the plane or via the aircrafts own A/C packs using pressurized air provided by the aircrafts auxiliary power unit (APU).
In many cases it's hot due to the big yellow hose being attached with a huge kink in it that prevents airflow, or the APU being too weak to provide enough air to the packs to provide good A/C.
Sometimes the APU on the plane isn't working. In that case we are using the air and electricity hookups from the jetbridge, or worst case if the jetbridge air is inop we have to use an external air cart to provide pressurized air to the packs for air at the gate as well as starting the engines at the appropriate time. One or the other, no doubling up. As stated above, in that case we'll kill the A/C, use the air cart to start one engine, disconnect the air cart, push back and then cross-bleed start the second engine and use the engines for A/C.
Normally after we push back from the gates, the air out of your vent cuts off for a period of time because we're using the air from the APU to start the engines instead of run the A/C. Once the engines are started, it is SOP to shut down the APU (to save gas/money) and let the engines provide the air for A/C. At idle RPM the motors tend to not provide enough air to make good A/C. A good Captain who's not super interested in making you uncomfortable to save the company money can run the APU to supplement air.
The A/C usually runs pretty damn good once the power comes up for Takeoff. By 10,000 ft you don't need much cooling, the temp at cruising altitude is -40 to -70F, so see the above discussion of pack operation at cruise altitude
In many cases it's hot due to the big yellow hose being attached with a huge kink in it that prevents airflow, or the APU being too weak to provide enough air to the packs to provide good A/C.
Sometimes the APU on the plane isn't working. In that case we are using the air and electricity hookups from the jetbridge, or worst case if the jetbridge air is inop we have to use an external air cart to provide pressurized air to the packs for air at the gate as well as starting the engines at the appropriate time. One or the other, no doubling up. As stated above, in that case we'll kill the A/C, use the air cart to start one engine, disconnect the air cart, push back and then cross-bleed start the second engine and use the engines for A/C.
Normally after we push back from the gates, the air out of your vent cuts off for a period of time because we're using the air from the APU to start the engines instead of run the A/C. Once the engines are started, it is SOP to shut down the APU (to save gas/money) and let the engines provide the air for A/C. At idle RPM the motors tend to not provide enough air to make good A/C. A good Captain who's not super interested in making you uncomfortable to save the company money can run the APU to supplement air.
The A/C usually runs pretty damn good once the power comes up for Takeoff. By 10,000 ft you don't need much cooling, the temp at cruising altitude is -40 to -70F, so see the above discussion of pack operation at cruise altitude
Posted on 7/1/22 at 8:35 pm to thelawnwranglers
quote:
On a flight AC didn't work on tarmac.
What Jet you were on matters. Altitude has nothing to do with it. All modern airliners are cooled by air packs. No freon involved, just supercooled air pulled off the compression section of the engines(or APU). Sounds like you might have been on a worn out regional jet. Tired engines that struggle to keep up with the southern heat.
quote:Correct. It all comes from outside obviously. All environmental control systems on airliners create pressure and control temperature. Some jets do it better than others.
How does pressurized cabin work is there outside air coming in? I guess it has to or we would die
Edit: I see Flyingtexastiger has given a much more detailed explanation.
This post was edited on 7/1/22 at 8:38 pm
Posted on 7/1/22 at 8:37 pm to thelawnwranglers
Delta pilot teaching you a lesson! He wants a raise and he wants it now
Posted on 7/1/22 at 8:45 pm to Cracker
.
This post was edited on 7/1/22 at 8:52 pm
Posted on 7/1/22 at 9:12 pm to thelawnwranglers
I just wanted to chime in. I am also a pilot. Decent explanations already exist in this thread.
Posted on 7/1/22 at 9:48 pm to thelawnwranglers
Pressurized cabin doesn’t mean no outside air is getting in. Bleed air off the engines system is used for cabin air. In an average jet there is completely “new” air every 6 or so minutes iirc.
Posted on 7/1/22 at 10:01 pm to thelawnwranglers
About 3000 to 4000 feet
Posted on 7/1/22 at 10:42 pm to thelawnwranglers
Ac at gate is external.
You won't get ac in the plane unless the engine is running.
You won't get ac in the plane unless the engine is running.
Posted on 7/1/22 at 11:01 pm to thelawnwranglers
As I understand it, planes don’t have AC like your car or home.
It uses bleed air from the engines, and mixes hot bleed air with bleed air that is has been cooled by expansion/compression (no refrigerant, literally just compressing the gas and dumping the waste heat overboard.)
When you are at the gate, it’s cooled by attached ground connections.
But if you are on the tarmac and they have to cut the main engines to save fuel, you lose pretty much all cooling. You are just powering fans recirculating air.
It uses bleed air from the engines, and mixes hot bleed air with bleed air that is has been cooled by expansion/compression (no refrigerant, literally just compressing the gas and dumping the waste heat overboard.)
When you are at the gate, it’s cooled by attached ground connections.
But if you are on the tarmac and they have to cut the main engines to save fuel, you lose pretty much all cooling. You are just powering fans recirculating air.
This post was edited on 7/1/22 at 11:02 pm
Posted on 7/1/22 at 11:11 pm to thelawnwranglers
Has anyone said bleed air yet?
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