HGU-55 HAWK Mk.66 / PC-21
The BAE Hawk canopy was equipped with an explosive cord (MDC - Miniature Detonation Cord) embedded within the Perspex. This device shatters the canopy simultaneously with the firing of the ejection seat.
Detonation of the cord causes a lot of sharp-edged acrylic laminated splinters, which risked to cut the "normal" HGU-55 visor bungees or even damage "exposed" visors, due to this the installation of the PRU-36 double visor assy.
It was mandatory to pilots approaching the Hawk to have at least one visor lowered.
Due to the same canopy configuration, the helmet, fitted with an HA-LP/PPB oxygen mask, currently represents standard equipment on Swiss AF Pilatus PC-21 advanced trainers.