keloutwest

Was on a flight last week in IAH (737-900) and the air conditioning was non-functional. It was about 90-something degrees outside, and the inside of the aircraft was probably around that temperature, parked at the gate during boarding. Pilot announced the issue but that it should resolve once we depart. Pushed back from gate, engines started, temperature on the aircraft remained VERY hot. Pilot announced it should cool down upon takeoff. People are fanning themselves with safety cards and the the experience is very unpleasant, but tolerable for a short time.

Get to runway, pilot announces an issue with weather radar, we pull off to side and they contact maintenance. Meanwhile, it is VERY hot on the plane, getting hotter, and the pilot announces they need to contact maintenance to see what to do (about the radar issue, not the air conditioning). Passengers are very upset, many gasps after the announcement, and some passengers are clearly now in distress. Everyone is dripping in sweat, and it's starting to get pretty rancid.

A few minutes later they announce we will return to the gate and determine whether they will let passengers deplane as maintenance works on the radar issue. Get to gate, they don't want to let passengers off. I confront the FA and after she asks me to be patient that they are evaluating what to do, I state "respectfully, this is not a negotiation, I and many others on the aircraft are demanding to be let off the plane immediately". Passengers who overhear start applauding. FA goes directly to pilot who allows passengers to deplane (most/all do).

Here is my question and issue: there was weather in IAH that day. What if there were a ground stop and/or no available gates to go back to? We would be trapped in a very hot, unsafe environment. I was seated in the emergency exit row, and my fellow passengers and I were discussing when it would be acceptable to pull the red handle and evacuate the aircraft. I considered this a serious safety issue that could have ended much worse. What is someone had a heat stroke? Panic attack? Are passengers in that situation allowed to self determine evacuating the aircraft when the crew was unable to resolve the issue?

I contacted UA Customer Service and asked that they confirm this aircraft be taken out of service until properly repaired and to please report the safety issue and confirm resolution and policy around this. As you can imagine, I received 5000 miles and an apology, with no confirmation or clarification around air conditioning maintenance policy (FWIW, I don't want the miles, I want this to never happen again to me or any fellow travelers - this aircraft should never have been allowed to board passengers let alone depart the gate.)

Thoughts on next steps? Are there rules around this sort of thing?

fumje

Technically speaking, this seems like non-functioning APU, which provides AC on the ground. Typically it is safe to fly without the APU. In flight, there's no need for AC given the air temperature at altitude. I don't know of any rules proscribing operation without APU in hot weather, although perhaps it would make sense to have some for extreme conditions. I believe there is capability to pipe in cool air while at the gate, although I also don't know of any rules requiring that they do this.

Probably good questions for the pilot thread.
United Pilot Q & A thread

IAH-OIL-TRASH

United does not owe you this. You can pretty much assume this is true : problem was noted and the situation resolved. I guess you must think pilots don’t report anything and if they do, United does nothing.

weibelt

No, passengers are not allowed to self determine to evacuate the aircraft.

I have had sweltering cabins on many international flights waiting to takeoff while baking in the sun.

mahasamatman

That is a fallacy. Do you think they just roll down the windows in flight?

prestonh

Ac is needed to cool off the bleed air which is hot from pressurization at altitude.

HNLbasedFlyer

APU units tend not to do great in hot weather. It’s a reality and why when you are in Vegas or Phoenix they often ask for the shades to be lowered on the ground.

Regardless, you aren’t entitled to a cool aircraft on the ground although it normally isn’t an issue.

In the air - you don’t have to worry about AC.

paperwastage

https://www.transportation.gov/indiv.../tarmac-delays.

You can raise a dot complaint asking what comfortable cabin temperature should be. Dot can only get a response from United (but it may not contain all the info you want).

prestonh

If an employee was on travel status at the time and a heat related injury occurred it would likely be wc claimable.

bubbashow

The 737900 is notoriously hot anyway. Same ac packs as a 737-700 with one extra circulator.

fumje

Thanks, I suppose that makes more sense when you point it out.

edit: I'm liking the explanation below better.

LarryJ

Aircraft do not have air-conditioners like what we have in buildings and cars. Those use the vapor-cycle with a compressor, evaporator, and refrigerant.

Aircraft use air-cycle machine called PACKs (Pneumatic Air Conditioning Kits) which are driven by high-pressure air from the engines or APU. There are Wikipedia articles that can explain more details on how PACKs work. The quick take is that nothing you know about how air-conditioners work helps you understand PACKs and how aircraft are cooled.

At the gate, you have pre-conditioned air (PCAir) which uses a conventional air-conditioner, mounted under the jet bridge, to provide cooled, or heated, air to the aircraft's conditioned-air ducting. The 737 does not do as well with PCAir as do some other aircraft and, in warmer conditions, it isn't unusual for the PCAir to be inadequate. I can only guess that his has to do with the configuration of the 737 conditioned air ducting which doesn't allow sufficient airflow. I'm also guessing that this is due to the design of the ducting dating back to the 1960, on much shorter airplanes, which couldn't be sufficiently modified due to available space restrictions as the aircraft was stretched. Again, that's just my guess based on over eight years of flying the airplane and my experiences from flying other aircraft. The shorter 737-700 does a lot better on PCAir than the longer 737-800/900. To make it work, you need a good PCAir source and you need to get it connected to the airplane BEFORE the cabin gets hot and before you load 150+ people to the airplane. If the cabin gets hot, even the best PCAir will struggle to catch up.

When PCAir is inadequate, we switch to the APU. The high pressure, and very hot, bleed air from the APU is routed to the PACKs where it is cooled and distributed to the cabin. We'd rather delay this until 10 or 15 minute before departure as the APU burns around 60 gallons per hour which is expensive and not environmentally friendly. Comfort comes before efficiency, though, and we'll switch to the APU early when needed.

During engine start, the high-pressure bleed air from the APU is needed to spin the engines' pneumatic starters. This is why the cabin air is greatly reduced during the engine start. The PACKs are switched off, during the start cycle, leaving only the recirculated air coming out the vents. That's about 60 seconds, per engine, on the NG and 150 seconds on the MAX, due to the Leap engine's longer start cycle.

The APU, or just the APU bleed air system, can be deferred under the aircraft's approved Minimum Equipment List (MEL). When it is, you don't have any bleed air to run the PACKs, prior to engine start, or to spin the engines to start them. In these situations, you use a "huffer" cart, which supplies high pressure air to the aircraft's pneumatic system to start one of the engines. This is called an Air Start. Later, after pushing back from the gate and taxiing away from the congested ramp area, you use bleed air from the operating engine, at an elevated power setting, to start the remaining engine. This is called a cross-bleed start and is usually accomplished during the taxi-out.

The process sounds simple. You use PCAir until you're ready to start the first engine. Disconnect PCAir and connect the huffer cart. Start the first engine. Disconnect the ground power and huffer cart. I'd imagine it sounds particularly good when you're sitting in an air-conditioned office writing procedure manuals. It often does not work out that way in practice. Huffer carts aren't used that often so the ramp personnel, while trained, rarely use them and these procedures so it doesn't always go smoothly.

Because of the locations of the pnuematic air hookup on the 737, the left engine must be started first so that the ramp personal can stay safely away from the running engine when disconnecting. The PCAir hose must also be disconnected and retracted so that it's not in the way of the running engine. This means that the time from PCAir being disconnected and the engine being started is extended. If there are any problems with the start, such as the huffer cart not providing sufficient air under load, the PCAir is already disconnected and the time spent without air is even longer. If we did Air Starts for every departure, as we did on the DC8 which never had an APU, it would likely run much smoother. But, we don't, and it often doesn't.

Once an engine is running, you'll have bleed air from it to run a PACK. Unfortunately, the bleed air from an engine at idle results in a PACK operating at reduced effectiveness. (This is also why the CRJ-200 is so hot on the ground in the warmer months even when the APU is operative) With a cabin that is already way too hot, it doesn't have a chance of catching up until after takeoff when the engines provide enough bleed air to run both PACKs at maximum effectiveness. When additional delays occur before departure, you're stuck with few options.

So, that's why it's hot.

The Captain really only has one option and that is to refuse the airplane and accept whatever delay that produces. It's a balance between an extensive delay or an uncomfortable cabin. The Captain has to make that decision well before departure and without knowledge of what problems and obstacles are going to pop up and how hot the cabin will get. With 20/20 hindsight, it's much easier to pick out the instances, like the OP's, when the aircraft should have been refused.

My last commute home was on an aircraft with an inop APU. In that case, everything went well. The airplane had PCAir connected quickly when it arrived which kept the cabin comfortable during boarding. The air-start process went well, and we had no delays taxiing and departing. It was a bit warm for a while, but not too bad. That's how it is supposed to work.

PhillyPhlyer40

I don't get why conditioned air shouldn't be a non-starter for any aircraft leaving the gate? Also, sometimes the air "dribbles" out of the vents...like they dont ever change the air filters...UGH.

fumje

If it's 15C and cloudy out, it's not a big deal.

But I could see sense in having rules for operating in, say >30C temperatures.

One thing to note is that the pilots are dealing with the same situation as the pax, so there is some implicit kind of self-regulation.

mduell

Not a safety issue, and this will happen again to other pax and crews.

Eventually they'd probably hand out water cups.

Also the gate aircon may have been inop as your gate as well. Usually they'll cool at the gate so it just warms up on taxi out.