The tail strike protection on the B777 consists of a tail strike assembly (TSA) and tail skid assembly. The TSA is an antenna with a two wires inside. So as when there is tail strike occurs, the antenna breaks causes the wires into open circuit which would trigger Tail Strike message.
The tail skid is the part that provide protection to the aft fuselage. If the tail touches the runway during take off, it will take the damage by absorbing the impact. There is a crushable cartridge build inside the absorbing cylinder that gets crushed as the cylinder conpression during the strike. During the impact, there is several thing may happen. A severe force impact absorb by tail skid can crush the cartridge inside. If more force have applied, there is a breakable fuse pin will break and will detach the part of skid assy from the aircraft structure in order to prevent further damages.
The severity of the impact can be determine by how much the indicator pins extend. The longer the pins is exposed, the greater the impact of the strike. If u do not know, the tail skid work together with gears. When the gears is down, the skid assembly will be extended. If the gears is up, the skid assembly will be retracted. That’s why you’re able to see on ground.
On a newer B777-300 series, you may not be able to see the tail skid assembly it’s not because of missing as the technology keep improving. The flight control logic computer latest software and data input that help on provide better aircraft centre of gravity for cargo and passenger loads. This does not only give a better protection of tail strike but also help the airlines to reduce several hundred weight.
Author – Lim Weeping ( Licensed Aircraft Mechanic B1.1)