On airliners, passenger seatbelts are simple lap belts. However, flight crews seem to have at least shoulder straps, and often five-point harnesses. Why do flight crew have more restraints?
ICAO Annex 6, Part 1 states:
6.2.2 An aeroplane shall be equipped with:
c) 3) a safety harness for each flight crew seat. The safety harness shall incorporate a device which will automatically restrain the occupant's torso in the event of rapid deceleration
It also confirm's Ben's comment that they are also meant to restrain an incapacitated pilot:
Recommendation.– The safety harness for each pilot seat should incorporate a device to prevent a suddenly incapacitated pilot from interfering with the flight controls.
I recall early in my glider training when I was about 17 before Id gone solo. My instructor used to keep his shoulder straps loose so I started doing the same.
On my 1st actual cable snap on the winch tow I whacked the stick forward and the glider went into -ve g. It was an open-cockpit glider with no canopy and I was half hanging out and only just managed to reach and get fingertips of one hand onto the joystick to pull myself back into the plane. I stabilised the glider, pulled my straps tight, but then found out my instructor behind me was not responding. I landed safely and then found out he was unconscious. He had bashed his head on the wing above him and passed out.
I always had my straps fastened properly after that incident.
There have been some "unusual attitude" instances where the crew have recovered the aircraft but would have possibly been thrown from their seats or unable to reach the controls through excessive G if not fully restrained.
In airliners, shoulder harnesses are not installed for passengers because:
- it is not not mandated by law
- it is too much for average passengers to deal with
- it requires money to install
- it is superfluous in a crash when compared to the same safety from a lap belt
Flight crew is required to use the shoulder harness (when installed) as it is the law (14 CFR 91.105):
(a) During takeoff and landing, and while en route, each required flight crewmember shall—
(1) Be at the crewmember station unless the absence is necessary to perform duties in connection with the operation of the aircraft or in connection with physiological needs; and
(2) Keep the safety belt fastened while at the crewmember station.
(b) Each required flight crewmember of a U.S.-registered civil aircraft shall, during takeoff and landing, keep his or her shoulder harness fastened while at his or her assigned duty station. This paragraph does not apply if—
(1) The seat at the crewmember's station is not equipped with a shoulder harness; or
(2) The crewmember would be unable to perform required duties with the shoulder harness fastened.
For passengers, while flying I feel fully restrained around the hips by a lap belt fully tightened- it would be more comfortable to have the belt load spread out. A full car seat belt compared to a lap belt allows you full motion. Its more likely the cost and difficult of having more anchor points on all seats especially when they spread them across the plane- a place to join the belt to the seat at higher point. They might also have to design the seat to handle its load being more spread out. Let alone having to work out if having such "improved" belts actually helps survivability with the greater risk of being unable to unclip.
The main function of a shoulder harness or five-point restraint (as opposed to a simple lap belt) is to provide upper-body restraint and keep the occupant's head and upper torso from flailing about during rapid decelerations.
If an airliner's about to crash, the passengers can be told to assume a brace position, which likewise keeps the upper body from flailing about, making a simple lap belt sufficient for safely restraining the passenger. The pilots, who have to (try to) fly the plane (or at least make sure it crashes as safely as possible), can't brace themselves, as this would prevent them from (e.g.) manipulating the flight controls; additionally, the area immediately in front of the pilots contains lots of potentially-injurious things, like the control yokes and various switches, buttons, dials, and levers, that the pilots' heads and upper torsos would smash into in the absence of upper-body restraint.
As a result of the more-injurious environment in front of the pilots and their inability to assume a brace position to protect their upper bodies in a crash, the pilots have restraint systems that provide upper-body restraint, such as shoulder harnesses or five-point restraints.