As Fabo said in your case the outflow valve in auto mode closes to let the pressure to remain inside.In the helios accident the packs were running, this situation provides positive pressure and fresh conditioned air in the cabin. The outflow valve in the helios was left in a position where the air pumped by the packs was a bit less than the air going out from the various holes in the cabin (outflow valves, drains, vents) this causes the pilots to not recognize the depressurization, oxigen will decrease slowly and the effects will be latent.I also think that when they heard the aural warning, they probably checked the bleeds and packs as they are the most probable cause.

With the outflow valve fully open outflow will always be greater than inflow and the cabin won't pressurize at all. It's true though that pack air flow will make the crew think all is well. However if you have a cabin altitude warning the first place you should look is the pressurisation panel, not the pneumatics panel.

With the outflow valve fully open outflow will always be greater than inflow and the cabin won't pressurize at all. It's true though that pack air flow will make the crew think all is well. However if you have a cabin altitude warning the first place you should look is the pressurisation panel, not the pneumatics panel.

Yes, they should look at the cabin altitude gauge, but, as it is a common mistake to leave the packs off after take off (not common, but this happens, and happened also with pax masks going out more than one time), or bleeds off, in a non normal situation, with hypoxia limiting your functions, the AUTO MAN ALTN knob (that most pilots will always find on AUTO) is what you search as a last option.

It is not possible that the outflow was fully open, in that case the outflow is much more greater than the inflow, and this causes a big cabin rate and it is almost impossible that a pilot climbing could not feel it.

Yes, they should look at the cabin altitude gauge, but, as it is a common mistake to leave the packs off after take off (not common, but this happens, and happened also with pax masks going out more than one time), or bleeds off, in a non normal situation, with hypoxia limiting your functions, the AUTO MAN ALTN knob (that most pilots will always find on AUTO) is what you search as a last option.

Hypoxia shouldn't have been significant at 10,000 cabin altitude when the horn first went off. Aircraft were, and still are safely operated at that altitude without oxygen.

It is not possible that the outflow was fully open, in that case the outflow is much more greater than the inflow, and this causes a big cabin rate and it is almost impossible that a pilot climbing could not feel it.

IIRC the valve was left fully open after testing by the maintenance technician. If the valve had been left nearly closed there may never have been a problem.

Hypoxia shouldn't have been significant at 10,000 cabin altitude when the horn first went off. Aircraft were, and still are safely operated at that altitude without oxygen.IIRC the valve was left fully open after testing by the maintenance technician. If the valve had been left nearly closed there may never have been a problem.

the aft outflow was partially openAfter the aircraft was returned into service, the flight crew overlooked the pressurisation system on three separate occasions: during the pre-flight procedure, the after-start check, and the after take-off check. During none of these checks did the flight crew notice the incorrect setting of the pressurisation system and did not set it back to "auto".^[8] The aircraft took-off at 9:07^[3] with the pressurisation system still set to "manual", and the aft outflow valve partially open.^[9]

Hypoxia shouldn't have been significant at 10,000 cabin altitude when the horn first went off. Aircraft were, and still are safely operated at that altitude without oxygen.IIRC the valve was left fully open after testing by the maintenance technician. If the valve had been left nearly closed there may never have been a problem.

In manual mode the outflow needs up to 20 seconds to open or close, if a technician (who did partially its job) want to test a system for operation, he could also only see the movement of the valve, without waiting the full open and close. It is wrong, out of procedures, but the test itself, for actuator operation will tell that motors are working.So, it is possible and it is that case, that the outflow valve was partially open. With a full open valve the cabin rate will be much higher and also the worst pilot, crew member, passenger will recognize it a lot before reaching 10000fts.Before reaching 10000fts the cabin was at 9000, 9500, 9900 for a lot of minutes, I will search for a dfdr readings if I can find it on the net, it will say us all the data including the outflow position.1 minute at 10000ft is different from 10 minutes, and different from 20 minutes, and the time play its rules.

I found the investigation report, I think you must read it, I found some info about the accident and there is a table with flight altitude VS cabin altitude.The decompression rate was similar to the aircraft rate, the warning sounded at around 12500ft of aircraft altitude, meaning that at that altitude the cabin was at 10000... The strange thing is that noone inside the plane found the cabin rate so strange... I made some ground tests on the pressurization systemand used the manual function to pressurize it with APU, if you play too much with the valve the rate becomes really fast uncomfortable...However, find the document here:http://www.moi.gov.cy/moi/pio/pio.nsf/all/F15FBD7320037284C2257204002B6243/$file/FINAL%20REPORT%205B-DBY.pdf

Couldn't get that link to work.Did do a bit more reading though. Still a strange accident - why did the crew keep climbing? At 10,000/12,000 there still wasn't much of a problem. Compounding a missed checklist item (pressurisation not in auto) by misinterpreting the warning horn, and then climbing to fl34. Also strange that the fa got to the cockpit, about 2 hours later. Just in time for the first flame-out. If he'd had a bit more time it would have been very intersting to see if he could have landed it - or at least pulled off a survivable impact with terrain.

We don't know exactly when he entered the cockpit for the first time, if I remember correctly. The only thing we do know, is that he was in the captain's seat when the aircraft hit solid ground. I may be wrong on this, but that's how I remember reading it...

Still a strange accident - why did the crew keep climbing? At 10,000/12,000 there still wasn't much of a problem.

Would you put your oxygen mask on for a takeoff configuration warning? If that's what you thought you had, you'd think there was a problem with the squat switches or flaps or something.They went down the rabbit hole and never got back out.

What I absolutely find strange is how both pilots did not recognize the fast pressure ratio, maybe a pilot could help me to understand it...

We don't know exactly when he entered the cockpit for the first time, if I remember correctly. The only thing we do know, is that he was in the captain's seat when the aircraft hit solid ground.I may be wrong on this, but that's how I remember reading it...

He entered at 8.48.52 (maybe GMT) CVR recorded the door chimes when he entered the code. (page 6 and 7 of the document). Then he tried to seat to the captain seat (seat adjustment noise), then he used the crew oxygen mask (noise from it)At 8:54 he did the MAYDAY (recorded only on CVR) with a weak voice, the engine number one was already flamed out.

Not quite true.... The newer 737's do indicate the difference between take off config and cabin altitude.I couldn't remember whether the pass OXY masks triggered the master caution or not, thanks for reminding me Andrea ;-)

There was an AD that mandated the addition of CABIN ALTITUDE warning lights, yes, but it still uses the same horn. MD SPEAKS the problem to you, thus eliminating the requirement to hunt the panel for a light in a situation where time is very critical.Best regards,Robin.

Would you put your oxygen mask on for a takeoff configuration warning? If that's what you thought you had, you'd think there was a problem with the squat switches or flaps or something.They went down the rabbit hole and never got back out.

If i hear the 'takeoff config' warning @12,000ft, which is also the pressurisation warning, with my ears popping strangely and me and my fo starting to feel dizzy...i'd put on my oxygen mask. Mistake shouldn't have been made in the first place, but having missed the problem at the checklist stage this was an eminently salvagable situation.

If i hear the 'takeoff config' warning @12,000ft, which is also the pressurisation warning, with my ears popping strangely and me and my fo starting to feel dizzy...i'd put on my oxygen mask. Mistake shouldn't have been made in the first place, but having missed the problem at the checklist stage this was an eminently salvagable situation.

Now you're using logic - something that captain was not. But, this is why we have to read that pressurization note every day. Did you check out his employment history? He changed jobs more often than I change my socks. His CRM was suspect, too. I wonder how he was to fly with.

When the captain called the company for the warning, another thing was happening, the OFF light of the equipment cooling (wich is normal if there is few airflow, that is the case of low pressure air, not sufficient to cool the sensor. That low pressure opened also the equipment cooling overflow valve (wich will be actuated with the differential pressure, it is a fully mechanical valve), causing a faster cabin climb.However, in the discussion the captain searched for the equipment cooling circuit breakers, thecnician said about the air conditioning panel, but captain stopped him and asked again for the breakers.Maybe both pilots, after this sound, at at least 2000fpm of vertical speed, searched for equipment cooling breakers, this moving their attention away from the main problem. Reading about the discussion, it is a bit confusing, maybe the pilots were not fully capable. I think they searched for a minute or 2, the master caution was already on for the equip cooling (wich turn on the OVERHEAD light on the recall), maybe they missed the OXY ON light because no alert from master caution wich was already on.Another point to add a "ding" at each master caution events :)As reported from the document, the pilots missed to check panel knob position at least 3 times in the checklist. Plus the time where the technician told about pressurization on AUTO position.Now I've not read the entire document, but in the section where is present the overhead panel picture, the document says that bleeds where both in off position, I need to check this on the document, as it was not mentioned in the causes.However, bleeds or packs off will reduce the life time in the cabin as there is no air exchange.