An Open Letter to Hollywood from an Aerospace Engineer

Short version: you clearly know nothing about how plane crashes happen. Please consult someone who does.

I have seen a number of plane crashes in movies and TV. This really shouldn't be a surprise; they are big, dramatic events, so you can burn a fair amount of your special effects budget (or with some careful use of models and stock footage, very little of it) in a nice dramatic scene.

Problem is, real plane crashes (even of light aircraft, much less the full sized commercial widebodies that the TV and movie industry prefers) are really rare, so people don't have much idea what they look like or what causes them.

Or, more to the point of what triggered this note, what can NOT cause them.

I have now seen it several times (most recently on a TV show): someone gets a firearm (sidearm or one-shot, note, not even a rifle) onto an airplane, and fires a round that punches through the sidewall, often at a window. This causes the sidewall to explode outward, decompressing the airplane and causing it to crash.

WRONG!

First off, there is actually no guarantee that such a round would penetrate all the way to the outside. Possible? Certainly. Probable? Depends on the round and exactly where it hits. A window is, granted, an easier barrier to beat than the sidewall/insulation/skin stack up.

But let's set that aside and say you do puncture the pressure vessel. What happens? Contrary to some perceptions aircraft at cruising altitude are not in a vacuum (if they were they couldn't fly). Nor is an aircraft cabin at full sea-level pressure during such a phase of flight. So there is MUCH less than one atmosphere of pressure difference between inside and outside. How much? Again, it depends. The 787 (which has not yes had a hull loss, much less a crash, that I've heard of and has a MUCH tougher skin) has a measurably higher pressure than other commercial birds out there and is still at less than sea-level pressure at cruising altitude.

Aircraft are designed to withstand depressurization through much bigger holes than even a shotgun with slugs could produce. Nor is the structure so weak that punching a hole will cause a secondary hull loss - again, designed and extensively tested for that. Shooting a hole in a window will break the window, and you will probably loose some of the 'glass' (it isn't) to secondary spalling, but the frame WILL remain. A round through the hull (assuming your bullet actually breaches the sidewall, the insulation, and still hits the skin with enough energy to break it) will expand even less.

So, the aircraft is depressurizing. There will be screaming, oxygen masks will deploy, etc. Will the airplane crash?

No.

The airplane WILL suddenly and (to the passengers) inexplicably dive. It will do so more steeply than anything most passengers have experienced outside of a roller coaster. This will not, however, be the first stage of a crash - it is a deliberate and carefully rehearsed action on the part of the flight crew to get the plane down to thicker air, where there is enough oxygen that people can breath it without passing out. See, those oxygen masks with the teeny little tubes and the bags they tell you may not inflate? That's temporary, supplemental oxygen. If you tried to breath that, and that alone, in a fully oxygen depleted atmosphere you would pass out. That's OK because as noted aircraft by definition do not fly in vacuum. There's always SOME oxygen outside the hull, and the pressure inside even after a full decompression won't be lower than the pressure outside. The oxygen system is designed to keep everyone conscious while the plane makes a worst case emergency descent (which can involve being stuck over the Himalayas and unable to descend to the desired altitude for a while).

So, the plane goes into a (by most people's definition, probably including your stomach's) steep dive for a few minutes, then... it levels off. Wow, we're really low now, we must be in danger of crashing if the pilot makes a mistake, right?

Wrong again. You're "low" by commercial cruising standards. You will, in fact, dive to under 10,000 feet. You might very well go down to 5,000. Plenty of margin for error.

So... we're fine?

Well, the pilot will have declared an emergency and will be looking for the nearest place to land before you even figure out what's going on.

Oooh! Emergency! So we're in great danger?

Again, sorry, no. You're in potential danger, and that's far too much for the FAA to allow. Commercial aircraft are designed to withstand any single failure without crashing (if you don't believe me, look up how many commercial widebodies have crashed throughout aviation history - and note that the worst aviation accident was on the ground!). By decompressing you've had one failure and used up your design margin, so you now have to land since the aircraft MIGHT not be OK if something ENTIRELY UNRELATED TO THE FIRST INCIDENT happened. Anything related to the first incident? We designed for that. Again, look at the crash statistics. We're good at designing for stuff.

So you CAN'T bring down a plane with a pistol?

Well, I can't say that, but your best odds are to shoot the pilot in the back of the head (while the autopilot is off, mind, which isn't for much of any given flight) and cause the co-pilot to panic for a minute, allowing the plane to get into an out of control condition which he can't recover from. Note that modern cockpit doors are "bullet proof". (I make a habit of using the quotes because it all depends on the bullet - a .50 BMG will hole a remarkable number of "bullet proof" items, but smuggling something that will fire THAT onto an airplane is beyond even my abilities. Yes I know how to smuggle a firearm onboard an airplane, I choose not to and I'm not going to say how on the internet.)

Huh. What if I shoot an engine?

Good luck. We design not only to fly on one engine, but to fly after one engine EXPLODES. Granted, that's a tough one, and especially if you were low at the time the pilot might not be able to recover. You still get better odds by shooting the pilot, though getting into the cockpit is non-trivial.

Uh... control cable?

Oooh, you did some homework! Yes, those cables (slowly becoming just more electrical wires) that turn the pilot's actions into flap, rudder, etc. movements are very imported for continued flight. Thus they are protected, dual-control, or can be worked around. A failure of a control cable would be a "single failure" so, say it with me! We designed for it. Besides, are you holding a set of blueprints while you aim?

Fuel tank?

Hollywood does like the "shooting a gas tank makes it explode" idea. Pity that's actually a low probability event (look up Mythbusters). Punching a hole in a tank does not inherently produce a spark to make fuel ignite. In fact we work VERY hard to ensure that there is nothing in or around a fuel tank that CAN make sparks (special coatings on fasteners, grounding wires all over the place, etc.). Bullets are typically made of lead and copper, neither of which is great for making sparks.

Despite our best efforts, accidents happen and people die. Over the years, however, we've made flying miles above the ground in an aluminum can filled with fuel, electronics, and other hazards safer than walking down the sidewalk. Again, look at the list of commercial widebody crashes. Note that the top ten usually includes the Tenerife incident, which was a ground collision, and a 2003 crash in Iran which was an IL-76 (a Russian design - the Russians just aren't as good as we are). You'll also usually see TWO losses to anti-aircraft missiles in the top 20 (Iran Air 655 in 1988 and KAL 007 in 1983). Sorry, we can't design for that. Depending on the list you may see 9/11. While the TSA is unlikely to stop another such attack, hardened cockpit doors and improved crew and flight procedures (thank you FAA, not TSA) will make such an attack VERY hard to replicate.

But even counting all those things that engineers can't design for, look at the list in total, no exceptions. Now look at the number of fatalities from car crashes, or from private aviation, every year.

We design well. Hollywood please take note.