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Common Fleet Reliability Issues
Please click on any of the topics below to find out more information
ALERT PROGRAM TOPICS
 Coding
Rate Calculations
Assigning Alert Values
Non-Traditional Performance Monitoring
Technical Analysis Topics
The Initial Technical Analysis
Root Cause Analysis
Corrective Action
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AVIATION RELIABILITY SERVICES - FLEET RELIABILITY |
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Fleet Reliability - Rate Calculations
Fleet sizes change. Flight schedules are seasonal. Stage lengths can vary from fleet to fleet - and sometimes from aircraft to aircraft. For these reasons, a simple count of aircraft system problems is not always an accurate indicator of aircraft reliability.
The two most common event rates used in the airline industry are: events per flight hour and events per departure. A less common rate is events per engine hour. Since there are several choices, which rate is the best one to use? The simple answer is – all of them.
If your alert program includes the monitoring of flight delays and cancellations (D&Cs), the obvious rate formula would be D&Cs per departure – a more math friendly rate would be D&Cs per 100 (or 1000) departures. After all, you are looking to define what types of problems cause flight schedule interruptions.
If your alert program monitors pilot reported problems (Pireps), you shouldn’t box yourself in by choosing only one type of rate. You should consider each aircraft system individually – and choose a rate that best defines how the system operates. Consider these examples:
1. Landing Gear Systems are only used twice during a flight – once during takeoff and once
while landing. Whether a flight is one hour or ten hours, the landing gear will only be used
twice. In this case, the only logical rate formula would be landing gear problems per 100 (or
1000) departures.
2. Hydraulic Systems are usually active only when the engines are running. For the most part,
hydraulic systems operate only during a flight. Therefore, the best rate formula would be
hydraulic system failures per 100 (or 1000) flight hours.
3. Auxiliary Power Units (APUs) are often run on the ground to supply electrical power and
pneumatics (for air conditioning) to a parked aircraft. They are also sometimes used during
overnight maintenance to power the aircraft when performing routine maintenance actions.
Therefore, actual usage may not be representative with either a flight hour or departure
rate calculation. The best rate would be APU failures per APU run time – which would require
the use of an hour meter on the APU.
In review, you should always try to use an event rate that is representative of the way the aircraft system operates.
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