Despite being cosidered an alternate equipment to the H-5 also to be used for jet aircraft, as officially mentioned in the " 1974 Piloten/Besatzungen (...) Zuteilungsliste" (Pilot and Crew Equipment Allocation List), this helmet was in use almost only with slow movers as Pilatus training/liaison/transport aircraft and helicopters. The shell is a standard "early" HGU-2, with the three holes present on top of the helmet crown.
Communication harness is the same ( less the mask/ boom mike switch) as fitted to Swiss H-5s. The installation is completed by (H-154/AIC) MX3678 (RH) and MX3679 (LH) earcups with spring loaded arms.
Installed on the "banana mount" is a French ELNO boom mike.
As a Swiss AF standard of the era, a British Mk.2 visor assembly is fitted to the helmet.
More on Swiss AF HGU-2 HERE
HGU-2 on Pilatus P.2.