Ok, but if it’s slaved to magnetic north without knowing where it is and compensating for the angular change as it moves about the earth, isn’t it going to drift off quite a bit if it doesn’t have GPS? And if it has GPS, what’s the point of being slaved to a compass?
I have trouble understanding how the hypoxia works. I’ve seen documentaries where they show the effects of hypoxia and I’d think that a trained pilot or aircrew would recognize the effects before they lost consciousness.
Isn’t there some way to monitor the pressurization and sound an alarm if it drops below a certain level?
I’m not sure that’s a good assumption. Airplanes have upgraded avionics installed all the time. I’ve seen airplanes built in the 1960’s upgraded to GPS nav and autopilot, and even “glass cockpits”
Yes, but on that particular airplane the flight attendant who wound up on the controls actually did have a pilot’s license. Although the consensus on the Dope is that being a private pilot wouldn’t give you much of an advantage over a total ignoramous in landing something like a big Boeing, the consensus is also that you have nothing lose by trying if things have really gotten that bad.
There are oxygen supply systems of one sort or another available for just about anything that flies. A Lear, given it’s altitude capability and the fact it is pressurized, would of course be required to have a proper oxygen supply system. There is the possibility that that system malfunctioned.
A slow loss of pressure will knock you out if you can’t get extra oxygen. If the mask isn’t working you’ve got only a very, very short period of time in which to figure out the problem and fix it - if you even notice you have a problem in time. Loss of pressure resulting in oxygen deprivation screws up your thinking before it knocks you out.
As backup, in case the GPS fails? Because GPS isn’t totally 100% reliable. It’s extremely reliable, but not perfect.
Sometimes - but onset of hypoxia can be subtle, and as I already said, one of the symptoms is impaired judgement.
Yes, of course. But like any other system, sometimes it doesn’t work.
Also - the alarm can go off just fine, but if your supplemental oxygen system isn’t working you’re still screwed.
The directional indicator itself is a dumb instrument. It is a circular display with a compass rose and it is aligned to local magnetic north. It doesn’t know where it is on earth, it just knows which way north is. Something like a Lear-jet would have a slightly more sophisticated type of DI called an HSI or horizontal situation indicator. This is a DI with a course bar overlayed to show your desired track, and normally a heading “bug”.
An HSI also doesn’t know where it is, but it knows where north is, and it can display information to the pilot so he/she can figure out where they are (normally a distance and bearing to a ground based navigation aid.)
The GPS knows where it is, but it is a brave pilot who puts total reliance on one piece of equipment. So the two are used in conjunction. Normally if flying reference the GPS, the GPS track would be shown on the HSI, and heading information would come from the DI.
There are other systems that airliners have used from well before the days of GPS which use accelerometers to detect minute changes in direction of the aircraft. Starting from a known position, the system can maintain a reasonably accurate position for a certain amount of time until it gets another position fix.
On an HSI, the course bar could be set to track reference to a particular navigational aid or a GPS track (if fitted), in this case it shows you how far off track you are, and you can set the autopilot to maintain the track for you along with your desired altitude by using the NAV and ALT modes.
Another way to fly a track is to have the autopilot in HDG mode, in which case it flies the magnetic heading you set with the heading bug. You can then maintain track by making your own adjustments to the heading bug and therefore the aircraft’s heading.
If the aircraft was setup up for GPS navigation you could have the autopilot fly the entire route including any turning points. On the other hand, if you are flying reference ground navigation aids such as VORs or NDBs, you need to manually change VOR frequencies and required tracks at the various turning points.
In the first case, if left unattended, the aircraft will fly the flight-plan as set in the GPS until it gets to its destination, it will then probably keep flying on the last track until it runs out of fuel. In the second case, it will fly the last heading or track the pilot had set before they became unconscious. This could be a heading quite different to the final track.
Whatever the heading is, it will be the correct magnetic heading for wherever they are on the earth (although the whole magnetic north thing doesn’t work in areas close to the magnetic poles.)
The symptoms of hypoxia such as feelings of euphoria, a tendency to focus on a single task, and an inability to think clearly, make it very difficult to self diagnose. Right when things are going badly, you start feeling that everything is just great.
There certainly is a way to monitor pressurization and provide a warning in case it drops. But it is not fool proof, and someone who is not trained to go on oxygen at the first sign of a pressurization problem may try trouble shooting first, and then succumb to hypoxia. Or the system may have failed, or not even be fitted.
Although all PC_Flyboy_SIM747_driver would have to do is get the aircraft down to 14,000 feet or so. Then pilots wake up, and everyone is happy again!
This could actually be accomplioshed by pushing a couple of buttons, and although the aircraft that come with MS Flightsim aren’t that good, there are add-on aircraft that have very realistic avionics. PC_Flyboy_SIM747_driver might know enough from his flightsim program to be able to get the plane to a safe altitude.
Well, the steward apparently was training to be a pilot, who knows how far along that path he had gone. However, as you say, what did he have to lose?
The report of the Helios accident is still not officially released but here is a leaked article which even if accurate is obviously much truncated.
I think the official report may be out next month but the Greek authorities seem to be dragging their heels on it for some reason.
Interesting that the airline concerned changed their name without waiting for the report to be published though.
My post was about the Helios crash, and if that leaked article I linked to is correct then everyone else on board were already dead. The aircraft had been flying at altitude for a couple of hours on autopilot.
I was just commenting that in a pressurisation failure incident. If someone got to the controls and on oxygen while the pilots were unconscious, they only need to descend the plane, not land it. Of course, all they really need to do is give some oxygen to the pilots.
I’ve been in the altitude chamber as part of my job in the military, and I can tell you that if it doesn’t happen rapidly the effects are insidious. They tell you to take your mask off and put it on when you start feeling the effects. There are always people that don’t realize what is happening to them and only put their masks back on when they are forced to, even after being told that it will be happening to them not 20 minutes earlier. That’s why there is always a monitor in the chamber with you.
If it was gradual they may never have known. I haven’t read the accident report, so I really have no idea if it was or not. But hypoxia is bad news if you don’t know it’s happening.
I think I understand how the effects of hypoxia can sneak up on a person, but I’m still having trouble w/ this.
There were at least two members of the flight crew who should have, at least, understood the effects. There should have been some warning device that made them aware of the oxygen/pressure loss, presumably before it became acute, but we must assume that this device failed. or was ignored? In addition I assume that there is an instrument that would have indicated the pressure loss, or was this inoperable/ignored also?
If I’m reading the after accident report correctly, it says that the emergency oxygen system appeared to have been operational, but unused.
It would seem that the aircraft systems were in poor condition and uninspected and/or both the pilots were totally incompetent?
I just don’t see how there could be this combination of system/human failure w/o some prior warnings, given the strict inspection/qualification requirements of commercial aviation.
I’t would be reassuring to hear that some heads rolled and some heavy fines were levied, perhaps even some licenses revoked and some tightening of regulations over this incident, but I’ve heard no such reports.
Are you talking about the Helios or Payne Stewert accident?
The NTSB didn’t find a definitive cause for the Payne Stewert accident, so it would be difficult for them to justify any metaphorical lynchings, and as far as I know, the findings for the Helios accident haven’t been released yet.
At any rate, you wouldn’t necessarily hear about changes made to regulations or procedures as a result of an accident unless the media decided it was particularly interesting to the public.
I echo Johnny, in that I can’t tell which accident you’re talking about, or if you mean both.
Even if you’ve been educated, even if you’ve been through training in an altitude chamber, hypoxia can still sneak up on you. Remember - one of the first things to go is your judgement. You aren’t aware of just how stupid you’re getting. Yes, it’s hard to wrap your head around this.
Or it worked and they paid attention but were unable to either get supplemental oxygen or get to a lower altitude in time to something to save their lives.
Is that Payne Stewart? The decompression occured suddenly in that accident, so whatever happened was quick. It could be they didn’t have time to activate the emergency oxygen system before passing out.
Because a definitive cause for the Stewart accident was never (as far as I know) determined it is entirely possible that the pilots were highly competant and did their best, and the aircraft systems were properly maintained to standard, and something went dreadfully, dreadfully wrong. The mere fact an accident happened does not automatically mean human incompetance (although that is certainly a factor to consider).
As for the Helios accident - last I heard, there was speculation that the emergency oxygen system had failed. At that altitude, you only get one chance to get it right. So - they depressurize. The pilots don their masks, expecting instant delivery of oxygen. But there isn’t any. They pass out. End of story (for them). Yes, certainly there are questions about maintenance of the pressurization and emergency O2 systems.
First of all, you are assuming human error - that is unfair to the pilots who may have done everything correctly but were not in a survivable situation. Or maybe they did screw up. Maybe it was a maintenance mechanic who screwed up. Maybe there was a factory defect in a crucial part. My point is that until the final report - and sometimes not even then - we don’t know what caused this.
To what point? If there is no human error, what would this accomplish, other than satisfying a human urge for revenge by scapegoating an innocent party. Given that the pilots involved are all dead, who do you fine? Their families? Why? The families wouldn’t be guilty, why would you punish them? Now, if it turns out that a mechanic failed in his/her duties then punitive measure might make sense, or if an airline or charter operator was engaged systematic violations I could see penalities.
Whose licenses? The dead pilots? Haven’t they been “revoked” as severely as possible already?
If the problem is that someone didn’t follow an existing regulation I fail to see how adding more regulation will solve the problem.
What Johnny said - you likely never will, because the mainstream media just doesn’t think the public is interested. But it’s not unusual for a pilot to point to a particular regulation and say “That one is because of accident XYZ”
I guess I was a bit vague on which incident I was referring to. I was thinking primarily of the Stewart A/C, but had the other one in the back of my mind.
You say it was a sudden decompression, that’s the first time I’ve heard that statement. Even then, isn’t there a requirement that at least one pilot be on oxy. above a specific altitude?
My referrence to revocation of licenses was directed at the people who owned/inspected/certified the A/C.
I do believe that any action taken would have been reported, due to the attention given to the original story, Stewarts celebrity status, and the unusual circumstances of the incident
It’s normally Jonno or Jonathan actually ;).
(Yeah, I know, you were thinking of Johnny L. A..)
Another thing to consider is that when first going on to oxygen, you can immediately feel a bit worse. This can lead some to assume the oxygen isn’t working, and take the mask off.
Sorry if I’ve confused the issue about which accident we’re talking about but I was trying to respond to dolphinboy’s question, and used the Helios accident which does have many similiar features of the Stewart crash.
I haven’t seen an authoritive source confirming that there was a problem with the oxygen supply. It seems that the aircraft had a history of pressurisation problems though and on the night prior to the flight the maintenance staff did some work on the pressurisation system and didn’t return the pressurisation mode selector to Auto from Manual (where it was for the ground tests) The aircrew failed to notice this on their pre-checks before flight.
.
The above quote was taken from here which does seem to have captured what happened without all the sensationalist reporting that went on at the time.
Hopefully the full report will be released soon.
The escort jet reported seeing frosted windows - although not conclusive, condensation is a feature of a sudden drop in pressure.
As they were ascending at the time, it is possible that the emergency occured before before they had reached that altitude and therefore there was not a pilot already on O2. The airplane continued to climb even after all contact was lost.
Well, that’s what the accident investigation is for - to determine if any particular party(s) was to blame. Although, since it was the FAA that decided to certify the Lear I’m not sure you can take that “license” away. However, there is precedent for reversing part if not all of an original certification (The Piper Tomahawk, for example, was originally certified for spins but after a serious of accidents that has been changed to “spins prohibited”.)
Sometimes accidents happen due to a strange chain of events unlikely to happen again, a possibility that should be considered.