One of the reasons gun control proponents have tried banning .50 cal rifles and other similar high powered rifle cartridges is due to the hypothetical threat to commercial airlines by terrorists. Granted as we’ve seen here it’s still incredibly hard to take out an aircraft with a semi-auto rifle which is why even .50 cal anti-aircraft emplacements have dual or quad guns.
I just want to thank LSLGuy for his informative, well-written posts on this (and on other airline-related topics). It’s always fun to see your perspective, as an industry veteran.
For decent effect you need to mount them on a speedy aircraft. 
LSLGuy’s posts are always on point and very informative.
Quite a few really good aviation threads have appeared here on The Dope.
I am thinking this
B17G’s came in shot to pieces from 8mm, 20 to 30mm cannon, 25 40 and 88mm flak etc, pieces missing and hanging off, engines shot out, and managed to land.
Aside from killing one person with a direct hit, i don’t think you are going to harm a 747 much, it has redundant systems, it can fly missing engines, it has 2 pilots, and you can not put out enough fire power fast enough to really compromise the thing with a hunting rifle, or even a fully automatic assault rifle.
Maybe if you have an long barreled M2 on a stable tripod mount, and a good frontal or rear low angle line of fire, or something like that, but that isn’t something that happens every day.
One 30 caliber hole in most any plane isnt going to cause much harm in itself.
remember, a lot of WWII planes were firing ammo in the 30 caliber range, and they found they needed to put in quite a few guns to take down enemy planes.
Aside from legal aspects (not to drift into the endless loop of gun control debates :smack: ) .50 caliber sniper rifles would also have a greater capability to shoot at airplanes on the ground from outside the security perimeter of an airfield, and they can fire so called multipurpose anti-material ammunition* with explosive and incendiary effect and a greater possibility of doing serious damage to a plane with one hit compared to either smaller caliber rifles or the ammo .50/12.7mm class machine guns fired say in WWII, Korea or Vietnam. Further speculating, it might be manageable for a very skilled shooter to hit an airplane from head or tail on with such a gun a few seconds after takeoff or before landing from head on or tail on, again from a position outside an airfield’s perimeter. That’s still a bunch of ifs though.
But as has been discussed, while plenty of jet (fighter and attack a/c) have been downed by cumulative 1,000’s of round and besides many cases of non-lethal hits by small arms/machine guns, the probability of a given ordinary rifle scoring a critical hit in a magazine’s worth of shots at a plane at significant altitude and speed and at any kind of crossing angle to the shooter, is extremely low.
I’m thinking that rather than aiming at a window, you should be aiming at the rear stabiliser. Break the hydraulics to that and the plane is in real trouble.
Odd, right? I was thinking about the idea of the golden BB that takes out the fan on the #2 engine on a DC-10 (or the military version, the KC-10). An induced version of United 232.
(Although I guess M-D made some changes to prevent uncontained engine 2 fan failure from completely destroying hydraulics.)
ETA: partly ninja’d by gnoitall.
Some older or smaller jets don’t even have hydraulics back there. For the rest there are two or three independent hydraulic systems. The two elevator halves, left and right are independently powered and move separately. Even if somehow gunfire jammed one, the other still works. Each half is powered by all the separate hydraulic systems and any one still functioning is enough to fly with. On my aircraft we can lose two of three systems completely and one of the two actuators on the remaining system on the horizontal tail & still fly pretty much normally. Ailerons and rudders have similar redundancy.
You’re probably thinking about United 232, the Sioux City Iowa DC-10 accident. The actual failure there was that all three hydraulic systems were holed, leading to loss of all hydraulics to all the flight controls. The plumbing was cut open by the #2 engine coming apart, which did happen in the tail. But the effects were felt all over the aircraft, even in the aileron control in the wings. One of the lessons learned from UA232 was not to place the lines from all the redundant systems too close together at any point in their routing around the aircraft. Although the area of destruction when that engine came apart was much larger than any single inert fast-moving bullet could cause. Something like a 20mm cannon shell, which explodes on impact would be a very different kettle of fish.
As further redundancy, the stabilizer trim mechanism uses an independent power source from the elevator & rudder. Typically one is hydraulic, the other electric. Flying just using pitch trim is very difficult and is likely to result in something kinda like what happened to UA232: A barely-controlled crash that may or may not have survivors. As has been discussed unto death they had very good skill and also unreasonably good luck.
EDIT: partial ninja by LSLGuy; my response was typed up while prepping my dinner…
No. Cabin altitude is not maintained at sea level (14.7psi); the energy required to maintain that pressure differential, and the additional structural weight to contain it, would not be economical.
At FL420 (a.k.a. ~42,000ft above sea level), the cabin altitude of the DC-10/KC-10 is about 8000ft or so. It’s been over 1.5 years since my last flight in the -10, and it was the flight engineer’s job to monitor/control the cabin pressure, so unfortunately I don’t recall exactly what the pressure differential was at that altitude.
Newer aircraft like the Boeing 787 and some high-end business jets do maintain a higher cabin pressure differential than legacy aircraft, acknowledging the physiological fact that pilot performance and passenger comfort are better at lower cabin altitudes.
You can’t aim at a moving target - you have to aim ahead of it. Well ahead, in the case of a fast-moving aircraft.
Even in large aircraft, hydraulic lines are relatively small in diameter, depending on their location within the hydraulic system. Comparatively speaking, pilots are a much larger target than a hydraulic line, with much more immediate results if hit.
Most aircraft (and ALL airliners) with hydraulically-powered flight controls have two hyd systems powering each control surface. Or, they have “split surfaces”; for example, the rudder and elevators of the DC-10/KC-10 have two parts - upper and lower rudder, and inboard and outboard elevator. The upper and lower rudders are powered by separate hyd systems, and the aircraft is still controllable in normal flight regimes with one rudder inoperable. Same with the inboard and outboard elevators - each pair is powered by separate hyd systems, and the aircraft is still controllable in normal flight regimes with one pair of elevators inoperable. Flying (and most importantly, LANDING) with hyd failures is a frequent training event for USAF KC-10 pilots in their quarterly emergency procedures simulator sessions, and probably for airline pilot simulator training as well (LSLGuy can confirm or deny airline pilot training for hyd failures better than I could).
So generally random rifle bullets are a minimal threat to the airframe.
However if the dread terrorist Drachillix (in my country I am a hero) decided to start plinking at an airliner near or on the ground to where I had a clear shot at the sides of the fuselage, I would imagine it would be a very bad day to be a passenger on said plane.
Yes. Hydraulic lines were rerouted, certain areas were given additional protection, and “hydraulic fuses” were installed in all three hyd systems. The fuses will shut off flow to the portion of the system downstream from the fuses when they sense well-above-normal fluid flow, effectively isolating the damaged part of the hyd system and preserving fluid volume for the intact parts of the system (analogy: placing a tourniquet on a badly-injured limb with arterial bleeding. Might lose the limb, but the person will [probably] not die of blood loss).
I don’t know why McDoug chose to call them “hydraulic fuses” - the rest of the industry calls them isolation valves.
Yes, and “drilling someone straight from asshole to ballcap” is now in my repertory.
Leading the target, you mean. I remember dogfighting in Aces High and judging the required lead was tough. Not only did you have to account for the velocity of the target but the network lag. But it’s best to minimise the angle of deflection, shooting either from behind or straight ahead.
In the early days of WWI, they tried to shoot down those rickety kites with shotguns, rifles and even handguns fired from the cockpit. They were very rarely successful.
The chance of a sniper getting a 747 in flight with a single shot is tiny.
Any excuse to trot out one of my favorite jokes from the Viet Nam era:
Cracks me up every time.
I’m pretty sure that story is related in Michael Herr’s “Dispatches,” and Herr says the exchange happened with a Huey door gunner. The exchange turns up in “Full Metal Jacket” between Joker and a door gunner; Herr wrote some of the dialogue.
The very first episode of Mythbusters I ever saw tested decompression myths.
How did they test an airliner losing pressure at 30,000’ feet?
They didn’t. They found a reasonably intact Airliner at a Bone Yard. Sealed it up tight, and after a few false starts, successfully pressurised it to 2 atmospheres. Because of course it’s the 1 atmosphere pressure difference between inside and out that’s important.
This is also the point where I decided I was goint to watch the hell out of this show.
Here’s the short version of what they found. - YouTube