11.18 On Board Maintenance Systems Flashcards
What does CMCS stand for?
Central maintenance computer system
What does the CMCS do? [3]
- Enables ease of reporting and fault finding
- Collects reports from different systems around the aircraft during flight
- carry out functional tests on the ground
What does a CMCS consist of? (5)
- central maintenance computers (CMC) in avionic compartment
- MCDU in flight deck as main interface
- a printer
- an ACARS connection to data-link the information to home base
- a digital computer in each system which is connected to CMC
What is the range of total number of complex systems connected to the CMC?
50 to 100 systems
What are CMC’s two modes of operation?
- reporting mode
- interactive mode
What is the reporting modes function? [3]
- Active during normal flight conditions
- Scans all connected aircraft systems and logs any fault info
- this can be displayed at any time on the MCDU or printed or sent to home base by ACARS
What are interactive modes function?
- can only be selected on the ground
- used for functional checks and fault investigation
What 3 different tests can interactive mode carry out?
- system test (computer test, no moving parts)
- Complementary test (moving parts)
- output test (engineer to interact with the procedure)
What does BITE stand for?
Built in test equipment
What 2 function does BITE have?
- Detect failures
- to perform system tests on the ground
When will BITE perform system tests?
Only when on the ground, Automatically when electrical power is switched on (power up test)
What does the CMCS have if the CMC were to fail?
Has a redundancy CMC which receives the same input data, and output becomes active automatically
What does the MCDU consist of? (3)
- a control area with multiple push buttons
- annunciator lights
- display area
When is the MCDU mainly used?
During flight to control the flight management system (FMS)
How can the CMC indicate that the MCDU is faulty?
Shows a FAIL annunciator on the MCDU
What are the buttons called on the side of the display area on the MCDU?
Line select keys
What does the display screen consist of? [2]
- 14 lines
- 24 characters max per line
What are the various locations on the MCDU display? (4)
- Title line
- label lines
- data lines
- scratch pad
What is the purpose of the scratch pad on the MCDU?
Used to enter alpha numeric data into data lines
What will the display show if the printer is not working, out of paper or in use by another system?
“No response” message
What happens when a system fault occurs, in regards to”report from last flight”?
- The fault is detected, the crew are alerted of the fault
- entered into tech log book
- The fault info, time date is memorised as a cockpit effect,
- can be read on the post flight report
When a fault occurs and is shown on the post flight report, what can help identify the correct system test to be performed?
Name of the system that performs the failure analysis (data source)
What does a cross check correlation do?
Ensures that the cockpit effect and the fault message belong together (time, date, ATA chapter and sub chapter are the same)
Can fault messages be reported without a corresponding cockpit effect?
Yes
What is defined as “the beginning of the flight”?
3 minutes after engine start
When does the flight “stop”?
During taxi into the terminal
What’s the difference between a hard and intermittent failure?
- Hard = permanent failure
- Intermittent = occurs one or several times during a flight, but not reported after landing
At the start of the next flight, what happens to the last flight?
It transfers from “last flight memory” to “history memory”
How many faults can the CMC store?
Up to 500 faults in the electronic library system (ELS)
When will faults only be stored?
If they occurred during flight
During CMC operation on the ground, what happens to any faults ?
They are listed on the MCDU or printed out, rather than being memorised
What prevents tests being allowed from running during flight?
The CMCS by special features
When can a system test only be trusted?
If all the components that could be responsible for the reported fault have “really” been tested
What appears on the MCDU when carrying out a complimentary test?
Any associated cautions and warnings regarding the system being tested
How often must the FMS navigation database be updated?
Every 28 days
How are new Nav databases loaded onto aircraft?
Airborne data loader (ADL), and can be transferred between 2 computers by “cross loading” the data
What must a portable data loader (PDL) be plugged into?
A specific plug in the cockpit
What 3 things can be used for monitoring the structure?(3)
- Fatigue meters
- strain gauges
- intelligent skins
What is a fatigue meter?
Instrument installed as close to the centre of gravity and the amount of G force that the aircraft is subjected to is recorded.
Results can be compared with proven limits
What are strain gauges?
Pieces of metal strips bonded to the structure at various places so current can pass through them.
The resistance of the strips change as the structure flexes and changes can be recorded
What is intelligent skins?
Fibre optic sensors embedded into the material of the skin, connected to signal processing units.
The ability to conduct lights will change if they are stretched or damaged
