The Second Best Place To Set a Bomb

An airplane I flew today had an oddly located fire extinguisher. While looking up the rules in CARS 525 on where the fire extinguisher has to be with respect to the pilot's duty station, I found some rules on airplane interior design that weren't there when I learned to fly.

(c) An aeroplane with a maximum certificated passenger seating capacity of more than 60 persons or a maximum certificated take-off gross weight of over 100,000 pounds (45,359 Kilograms) must comply with the following:
(amended 2010/06/16; no previous version)

    (1) Least risk bomb location. An aeroplane must be designed with a designated location where a bomb or other explosive device could be placed to best protect flight-critical structures and systems from damage in the case of detonation.

According to this FAA document the Least Risk Bomb Location (LRBL) has been a thing since approximately 1972. The crew should be aware of the LRBL, but we can be forgiven for not knowing, as the guidance document includes a prohibition on marking it with cute international graphics or bilingual block lettering saying something like "place unattended bombs here." For more information on determining the best location of an LRBL, you may consult a document entitled “DHS Recommended Least Risk Bomb Location Procedures for Airlines,” Sensitive Security Information (Limited Distribution). The FAA will need your letterhead and an e-mail address. I hope they do more than glance at the letterhead and go, "ooh, it's embossed, and someone used expensive design software on this, they must be a legit airline. Quick, e-mail them the secret LRBLs." Probably they have more secure procedures than that, but the whole letterhead thing is so quaint that I had to make fun of it.

If you don't have a need to know, or a fancy letterhead, you can still find out about LRBLs. The public document is interesting enough, with little diagrams and recommendations on how the LRBL should work. If you click through to look a the document, don't forget to scroll down to the name of the person responsible for it, and imagine how much fun he has at airports when he's "randomly" selected for special screening based on his name, and then they discover his carry one is full of Sensitive Security Information about where to put bombs on airplanes. Whatever city he lives in, that's where the meetings are.

The airplane I fly does not have a passenger seating capacity of more than 60 persons. Were we to discover a bomb on board, I would direct it to be thrown out the emergency exit. Such a measure would be an extreme emergency procedure for me, but its physically impossible to open an exit on a pressurized aircraft in flight, because the exits are plugs held in place by the pressure. The only way to open one would be to blow it up. The implication of the document is that that's kind of what some LRBLs do. It also points out that decompression is less harmful if it's not done explosively, so I imagine the "oh no there's a bomb on board" procedure involves an emergency descent and controlled depressurization. The descent would be so that by the time the airplane was depressurized and the oxygen in the generators was exhausted, the ambient oxygen would be sufficient to sustain the surviving passengers.

    (2) Survivability of systems:
        (i) Except where impracticable, redundant aeroplane systems necessary for continued safe flight and landing must be physically separated, at a minimum, by an amount equal to a sphere of diameter
        D = 2 v (H0 / P )
        (where H0 is defined under 525.365(e)(2) and D need not exceed 5.05 feet (1.54 metres)). The sphere is applied everywhere within the fuselage limited by the forward bulkhead and the aft bulkhead of the passenger cabin and cargo compartment beyond which, only one-half the sphere is applied.
        (ii) Where compliance with subparagraph (c)(2)(i) of this section is impracticable, other design precautions must be taken to maximize the survivability of those systems.

I think that is meant to imply that if you want to take out redundant systems, you'll need more than one bomb. Plus I'll throw you overboard with your bomb.

    (3) Interior design to facilitate searches. Design features must be incorporated that will deter concealment or promote discovery of weapons, explosives or other objects from a simple inspection in the following areas of the aeroplane cabin:
        (i) Areas above the overhead bins must be designed to prevent objects from being hidden from view in a simple search from the aisle. Designs that prevent concealment of objects with volumes 20 cubic inches and greater satisfy this requirement.
        (ii) Toilets must be designed to prevent the passage of solid objects greater than 2.0 inches in diameter.
        (iii) Life preservers or their storage locations must be designed so that tampering is evident.

What and ruin the plot of so many bad airplane movies? At least there's no rule about disabling the secret passage out of every airplane washroom into the giant avionics bay. I think the life jacket one is interesting. I've never noticed the lifejacket pouches to appear particularly tamper-resistant.

(d) Each chemical oxygen generator or its installation must be designed to be secure from deliberate manipulation by one of the following means:
(effective 2015/03/20)

    (1) by providing effective resistance to tampering,
    (2) by providing an effective combination of resistance to tampering and active tamper-evident features,
    (3) by installation in a location or manner whereby any attempt to access the generator would be immediately obvious, or
    (4) by a combination of approaches specified in (d)(1), (d)(2) and(d)(3) of this section that the Minister finds provides a secure installation.

(e) Exceptions. Aeroplanes used solely to transport cargo only need to meet the requirements of (b)(1), (b)(3) and (c)(2) of this section.
(effective 2015/03/20)

I haven't yet seen a bad airplane movie in which the bad guys repurpose the oxygen generators as poison gas grenades, but maybe it was so awesome I forgot.