Extreme pressurization

[Flying Illini]

One of our Falcon 20's had just come out of a 2A check (we do most maint. in house) and I was one of the pilot's assigned to it's return to service flight check. It was myself, the captain, and two mechanics who were to document the flight and confirm that items and previous write-ups had been fixed.
Anyway. I was the FP. The main item we were to check was the pressurization since the outflow valve had been sent out for service.
Everything normal up to liftoff. We take-off, gear up and locked and that's when it starts. The cabin is pressurizing...rapidly. The differential is already climbing through 3 and the cabin Alt. is decending through -1000'. And things are getting painful (in the ears). I take over the radio and continue flying as the captain tries desperatly to control the problem. I inform ATC that we are stopping our climb at 3000 and we would like to stay on our current heading. No prob.
Meanwhile, the cabin is now showing a 6psi differential and a cabin ALT of well below the -1000 scale, but if the scale continued we would be in the vicinity of -2500' CABIN ALT!! The thing is running away from us and we have no control. We hit the DUMP switch but nothing happens, we go to manual on the pressurization and starting running it with the cherry picker, but it does nothing, we even flipped the ram air switch but nothing happened (of course, too much pressure in the cabin, but we were trying anything!) THe only thing left to do was to shut off the bleed from the APU (aircraft bleed wasn't engaged yet). I did that and things stabilized. The cabin stopped descending and the differential stopped climbing. One of the mechanics on board is saying that he can't hear a word that we are saying (later on the ground when he could hear again he said all he could hear was cracking and popping in his ears. He could see our mouths moving but couldn't hear us...and he was in the jumpseat).
We figured if anything, the cabin would leak back up...but it was happening slowly. The other mechanic went to the lav area and pulled a panel to get to the outflow valve. Once there he opened it manually and the cabin finally started to climb! Once we got this sorted out, we came back and landed. The whole thing lasted just 9 minutes but it felt like much, much longer.

Just my fun day! Here's a question...should I be concerned about any health effects? We were at negative altitudes for quite a while. It felt like someone had their hands on both sides of your head and were squeezing. Rather uncomfortable.

 

[gear_guy]

You are fine since the Diff. PSI never even got to max diff. That is what you were feeling. The diff press was rapidly rising and you couldnt valsalva fast enough to keep up with it. Even if it did go beyond max diff., it would have either opened a relief valve or the fuselage would have given way(not good). Sounds like everyone acted together to solve a problem. Good job! The only thing I would be asking is why did'nt the dump valve work? Is it not tied to the APU bleed systems?

 

[Flying Illini]

"Why didn't the dump valve work?"

That was our main question after we landed and conferenced with all of our maint. guys. They don't know but by the time we left there were 5 guys going through books/diagrams/etc. They will figure it out and when I know I will make a mention of it here.

 

[Flying Illini]

At what PSI do you start considering the possibility of getting the "bends?" Is it even possible to reach that PSI in an aircraft if you were in a situation similar to ours? Once we hit 9. something the relief valve would have (hopefully) popped and the cabin would then depressurize.

 

[CLCAP]

At what PSI do you start considering the possibility of getting the "bends?" Is it even possible to reach that PSI in an aircraft if you were in a situation similar to ours? Once we hit 9. something the relief valve would have (hopefully) popped and the cabin would then depressurize.

No way of getting the bends!! When Scuba diving, you add one atmnospheric pressure every 33 eet or so - meaning that 9 psi would corespond to about 22 feet of water. I think you would have to spend MANY hours at that depth in order to be able to develop the bends (if at all) on the way up.

 

[GravityHater]

Why stop the climb? Wouldn't higher get you some relief at least?
I think the bends are when you DE pressurize, not overpressurize.

 

[wmuflyguy]

climbing would have probably jsut increased the pressure differential, and had no effect on teh actuall cabin alt.

 

[Lead Sled]

should I be concerned about any health effects? We were at negative altitudes for quite a while. It felt like someone had their hands on both sides of your head and were squeezing. Rather uncomfortable.

Nothing too serious. I would expect a rather extreme case of diarrehea (aka Turkey Squirts). The onset should be within 48 hours of exposure and the duration should be no more than 8 days. Good luck.

'Sled

 

[Illini Pilot]

no problem with decompression sickness i would guess...first off as one person said, the partial pressure increases very rapidly in water, probably didn't come anywhere near it. also, since it was a slow-ish de-pressurization, any nitrogen dissolved in your tissues most likely was expelled slowly (unlike scuba diving when a fast ascent from lower depths can lead to the nitrogen remaining dissolved)