MORA  Minimum Off-Route Altitude 
MOS  Metal Oxide Semiconductor 
MOSFET  Metal Oxide Semiconductor Field Effect Transmitter 
MOU  Memorandum Of Understanding 
MP  (1) Middle Plug. Identifies the plug position on the 
rear connector of an avionics unit. 
(2) Main Processor 
MPEL  Maximum Permissable Exposure Level 
MROSE  Multiple-tasking Real-time Operating System 
Executive 
MRR  Manufacturing Revision Request 
MS  Millisecond 
MSB  Most Significant Bit 
MSCP  Mobile Satellite Service Provider 
MSD  (1) Most Significant Digit 
(2) Mass Storage Device 
MSG  Message 
MSI  Medium Scale Integration 
MSL  Mean Sea Level 
MSP  Mode S Specific Protocol 
MSSS  Mode S Specific Services 
MSU  Mode Select Unit 
MT  Minimum Time 
MTBF  Mean Time Between Failures. A performance figure 
calculated by dividing the total unit flying hours (air-
borne) accrued in a period of time by the number of 
unit failures that occurred during the same time. 
Where total unit hours are available,this may be used 
in lieu of total unit flying hours. 

MTBR  (1) Mean Time Between Removal (2) Mean Time Between Repairs. A performance fig-ure calculated by dividing the total unit flying hours accrued in a period by the number of unit removals (scheduled plus unscheduled) that occurred during the same period. 
MTBUR  (1) Mean Time Between Unscheduled Removal (2) Mean Time Between Unit Replacements. A perfor-mance figure calculated by dividing the total unit fly-ing hours (airborne) accrued in a period by the num-ber of unscheduled unit removals that occurred dur-ing the same period. 
MTC  Maintenance Terminal Cabinet 
MTD  Maintenance Terminal Display 
MTF  Maintenance Terminal Function 
MTI  Moving Target Indicator. This type of radar display will show only moving targets. 
MTM  Module Test and Maintenance 
MTMIU  Module Test and Maintenance Bus Interface Unit 
MTTDA  Mean Time To Dispatch Alert 
MTTF  Mean Time To Failure. A performance figure calculat-ed by dividing the summation of times to failure for a sample of failed items by the number of failed items in the sample. The same item failing N times consti-tutes N failed items in the sample. This is different from mean time between failures since no allowance is given to items that have not failed. 
MTTM  Mean Time To Maintenance. The arithmetic mean of the time intervals between maintenance actions.