HMI  Human Machine Interface 
HMOS  High Density Metal Oxide Semiconductor 
HOW  Hand-Over Word 
HP  High Pressure 
HPA  High Power Amplifier 
hPa  hecto Pascal 
HPC  High Pressure Compressor 
H-Plane  The H-Plane is the plane in which the magnetic field 
of the antenna lies. The H-Plane is perpendicular to 
the E-Plane. 
HPR  High Power Relay 
HPSOV  High Pressure Shutoff Valve 
HPT  High Pressure Turbine 
HSI  Horizontal Situation Indicator. An indicator that dis-
plays bearing,glideslope,distance, radio source, 
course and heading information. 
HSL  Heading Select 
HSR  High Stability Reference 
HUD  Heads Up Display 
HVPS  High Voltage Power Supply 
HW  Hardware 
HX  Heat Exchanger 
HYD  Hydraulic 
HYDIM  Hydraulic Interface Module 
Hz  Hertz (cycles per second) 
I 
IACSP  International Aeronautical Communications Service 
Provider 
IAF  Initial Approach Fix 
38   

IAOPA  International Council of Aircraft Owners and Pilots 
IAP  Instrument Approach Procedure 
IAPS  Integrated Avionics Processing System 
IAS  Indicated Air Speed 
IATA  International Air Transport Association 
IC  (1) Intercabinet 
(2) Integrated Circuit 
ICAO  International Civil Aviation Organization (Montreal)