Saturday, March 7, 2015

The Case for the South Indian Ocean: Part 1

In my previous blogs, I outlined two key kinds of aircraft incidents which I believe are clues to what happened to MH370. In the decompression/non-pressurizing situations I have two observations: people apparently can survive at least 2 hours at 34,000 (although unconscious), and at higher altitudes (above 40,000 in the Payne Stewart accident), it is unsurvivable.

Facts are important when making conjectures about MH370.

One of my favorites was a Twitterverse claim the US Navy hid MH370 in an underground/water secret hangar on Diego Garcia. When asked about the kind of construction required to put such a monstrosity on a tiny sea level atoll (you’d need a really deep hangar, a really long ramp, or some Gru-like elevator system, and a way of getting air down there), I was assailed for my stupidity, called a troll (whatever that is), then summarily blocked by some Twitter users.

According to those theorists, MH370 was in an underwater Diego Garcia hangar simply because—well it just HAD to be. And of course, you know, the US government can do such things. Obviously.

Back to the decompression/depressurization issue. There are two types. An explosive one. It’s sudden, violent, and normally without warning. That’s not what happened on MH370. If a someone depressurized the cabin then there’s only one way to do it. The automatic pressurization system had to be switched to a manual mode, and the cabin had to be raised. In pilot jargon, “climb” the cabin.

On the Boeing 777 are two big plate-like valves. These are the outflow valves which control the cabin pressure of the airplane. They’re constantly adjusting how much air leaves the cabin in order to maintain a comfortable altitude. In Boeing-speak: “Cabin pressurization is controlled by regulating the discharge of conditioned cabin air through the outflow valves.” Typically when you’re flying on a passenger aircraft, it’s like being in, say, Denver, Colorado. There are certainly many cities around the world at higher elevations, but aircraft cabins are generally maintained in the 5000-6000’ range.

The crew can directly control the position of the outflow valves using the manual mode, bypassing all the protections and controls offered by the aircraft’s computers. It’s provided in case the computers wander off the reservation. To take manual control of these valves, it’s a deliberate action. It requires pushing two buttons on the overhead panel for each valve, then moving two more switches to open the valves. Air then leaves the cabin until the inside of the cabin is at the same pressure as the outside. It takes some time for all this to happen. The Boeing manual is silent on just how long, presumably, because there are many variables involved.

The short version: depressurizing a Boeing 777 can’t be done accidentally.

At really high altitudes, it’s always subfreezing on any scale. Flying at 35,000 the standard temperature would be -55° c. For my American readers, that’s -67° f. It’s really chilly. That’s not to suggest that’s how cold it would get in the cabin after decompression. Remember air LEAVES the cabin in this event. As the air leaves the cabin the remaining air expands. It’s an unassailable law of physics. It will get really cold. The chilly outside air at that altitude will eventually be a factor, but it won’t happen quickly.

As I contemplate this part of the MH370 mystery, IF the cabin were decompressed to incapacitate and eventually kill people, it will take time, and the cabin needs to be above 35,000 feet for some duration to be fatal.

Remember those plastic yellow cups which provide oxygen for, as the flight attendants soothly murmur “in the unlikely event of an emergency”? They are deployed automatically when the cabin reaches about 13,500 feet pressure. There’s a crew control to manually DEPLOY the oxygen masks, but there is no way to prevent the oxygen masks from dropping. There’s no plausible scenario in which you’d want to stop masks from being presented for the passengers’ use.

If one wanted to kill potential people who would attempt to thwart your control an aircraft (read: passengers), you’d need a well-thought out plan, and you’d need time. Lots of it.

The passengers will get their 12 minutes of oxygen. What about the flight deck crew? They have a very different source of oxygen. It comes from an O2 tank designed to provide oxygen on demand through four masks available in the cockpit. Read that again. Four masks. There are four seats for pilots in the B777. Two obviously for the folks all the way at the pointy end of the airplane, and two observer seats (called jumpseats). Oxygen must be sufficient to provide long-term use to the flight deck, no just for a pressurization problem, but in case of smoke or fumes in the cockpit.

Pilots get much more than 12 minutes. They get a lot. For all four. When there’s only one pilot inhaling oxygen meant to supply four, you can go a really, really long time. How long? No clue, actually. But it would be measured in hours.

Hours needed to fly far away. Like a distant ocean.

Let’s revisit my discussion about pilot suicide. It happens. History documents that when pilots want to kill themselves, they nearly always do it alone. They await a chance to be by themselves in the cockpit, or concoct a reason to send a pilot out of the cockpit. It’s harder to fly an airplane into the ground when the other pilot is not on the same page as you are.

How do we know this? Simply because these suicide accident scenes are either found quickly, or the watery remains of the aircraft are found and recovered. Accident investigator’s have a lot of tools at their discretion. The cockpit voice recorder (CVR) tells a lot of what happened in the cockpit, and the digital flight data recorder (DFDR) tells them what happened to the airplane. Control inputs, speeds, attitude are but a few of the hundreds of data inputs in modern jet aircraft. Even when the suicidal pilot disables the the CVR/DFDR by pulling circuit breakers (CB) there are clues left.

These clues are often related to the fact that the recorders go strangely silent just before the airplane goes into a nose dive. If the DFDR circuit breaker is pulled first, there are tell-tale sounds (or lack of them) that suggest what happened. A CB doing circuit breaker stuff makes a distinctive “pop” which does not occur when a pilot pulls it.

And of course, there’s often radar data associated with the suicidal dive. DFDR/CVR goes dead. Plane heads like a lawn dart to the ground minutes later (as recorded on radar), and recovering the shattered aircraft parts will show there was no control issues leading up to the plunge. How that forensic study is done is not part of my discussion. It is amazing science though.

Any pilot who is a student of the industry (as I am), knows that the rare (very rare) suicide is eventually uncovered. Especially when you have an airplane part to look at. Even shattered ones. If you have a perceived reputation to uphold, family members to protect, and wish not to be forever known as a suicidal pilot, you don’t want your plane to be found to be subjected to forensic investigation.

What about that suicidal plunge? Why that?

Simple. You don’t want it to hurt.

There are no recorded suicides (I’m aware of) in which the pilot makes some kind of half-hearted attempt to land the airplane in a really bad way. I remember when I was a private pilot, I took a buddy of mine up flying in a small Piper single engine aircraft. I’ll never forget what he said.

“If something goes badly, nose it over. I don’t want to lay in a hospital bed for months.”

As a professional pilot however, I can tell you that when something goes badly, I’ll be fighting to save the aircraft, the passengers, and myself, all the way to the end. I’d never give up. I’d try to find a way to fix the problem, and never accept failure.

As famous stunt pilot Bob Hoover once opined, “If you're faced with a forced landing, fly the thing as far into the crash as possible.”

True dat.

Let me take all of this and put it together for a SIO scenario.

I believe that MH370 was flown to the remote part of the SIO for one reason, and one reason only. To hide the crime. To fly that far requires incapacitating all non-participants so they can’t stop you. In order to do that, you have to depressurize the cabin, and you need time for that that to work.

Additionally, if you are going to hide the crime, you need to disable all the noisy electronic stuff on the airplane. All the things that report your location, and all things that communicate to the outside world.

And you have to do that while evading, or at the very least, attempting not to draw attention to yourself on radar. You have to get outside of the ever-watchful eyes of not only ATC radar, but known military radar looking for inbound invaders.

Do do this, a great time to do it would be at night. Even better, late at night, preferably leading into the weekend when minds are dulled, and thinking more about weekend fun.

NEXT: The Case for the South Indian Ocean: Part 2.


  1. Ed I was giving some technical thought to your comment about cooling of the cabin air during a possible intentional depressurization. If we look at Wikipedia Joule-Thompson Effect we can see N2 J-T coefficient around 0.2 deg C per bar and air (79% N2) would be about 0.25 deg C per bar at 1 bar and room temp. I am rusty on this but looks like we'd only be talking a very small temp change due to adiabatic expansion. Not being an aerospace engr, I assume cabin cooling could happen due to less heated air coming into the cabin, due to heat losses to the outside.

    1. OK I was wrong...
      Looks like one equation for aircraft cabin depressurization temperature is:
      so that would say T2~=-20F air temp (yikes) but if the depressurization rate was not very rapid, then the temperature could stay more constant due to heat exchange with the surroundings, and I presume the pilot could "turn up the heat" to mask the cooling effect. see PHYSICS and ENGINEERING OF RAPID DECOMPRESSION Haber/Clamann