The following category codes are mainly for the use of RMAs. However, reporters may use this categorization as a reference for common causes of LHDs.
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A
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Flight crew failing to climb/descend the aircraft as cleared
Example: Aircraft A was at FL300 and assigned FL360. A CLAM alert was seen as
the aircraft passed FL364. The Mode C level reached FL365 before descending
back to FL360.
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B
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Flight crew climbing/descending without ATC Clearance
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C
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Incorrect flight level provided due to incorrect operation or interpretation of airborne equipment (e.g. incorrect operation of fully functional FMS, incorrect transcription of ATC clearance or re-clearance in FMS, flight plan followed rather than ATC clearance, original clearance followed instead of re-clearance etc.)
Example: The aircraft was maintaining a flight level below the assigned altitude.
The altimeters had not been reset at transition. The FL assigned was 350. The
aircraft was maintaining FL346 for in excess of 4 minutes.
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D
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ATC system loop error; (e.g. ATC issues incorrect flight level clearance or flight crew misunderstands flight level clearance message.)
Example: All communications between ATC and aircraft are by HF third party
voice relay. Aircraft 1 was maintaining FL360 and requested FL380. A clearance
to FL370 was issued, with an expectation for higher levels at a later point. A
clearance was then issued to Aircraft 2 to climb to FL390, this was correctly read
back by the HF operator, but was issued to Aircraft 1.
The error was detected when Aircraft 1 reported maintaining FL390.
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E
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Coordination errors in the ATC-to-ATC transfer of control responsibility as a result of human factors issues (e.g. late or non-existent coordination of flight level)
Example 1: Sector A coordinated Aircraft 1 to Sector B at FL380. The aircraft was
actually at FL400.
Example 2: The Sector A controller received coordination on Aircraft 1 for
Waypoint X at FL370 from Sector B. At 0504 Aircraft 1 was at Waypoint X at
FL350 requesting FL370.
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F
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Coordination errors in the ATC-to-ATC transfer of control responsibility as a result of equipment outage or technical issues (e.g. late or non-existent coordination of flight level)
Example: Controller in FIR A attempted to send AIDC message to coordinate
transfer of aircraft at FL320. Messaging was unsuccessful to contact
adjacent FIR by telephone fail. Aircraft contacted adjacent FIR without coordination
being completed.
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G
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Aircraft contingency event leading to sudden inability to maintain assigned flight level (e.g. pressurization failure, engine failure)
Example: Aircraft 1 descended from F400 to F300 with a pressurisation issue.
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H
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Airborne equipment failure leading to unintentional or undetected change of flight level
Example: Aircraft 1 cruising at FL380. ATC receives alert indicating aircraft
climbing through FL383. Flight crew advises attempting to regain cleared level
with autopilot and navigation system failure.
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I
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Turbulence or other weather related causes leading to unintentional or undetected change of flight level
Example: During the cruise at F400, the aircraft encountered severe turbulence,
resulting the aircraft descending 1,000 ft without a clearance.
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J
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TCAS resolution advisory, flight crew correctly climb or descend following the resolution advisory
Example: Aircraft 1 was cruising at FL350. Flight crew received "Traffic Alert" from TCAS and almost immediately after an "RA Climb" instruction. Flight crew responded and climbed Aircraft 1 to approx FL353 to comply with TCAS instruction. TCAS display indicated that opposite direction Aircraft 2 descended to approx FL345 and passed below Aircraft 1.
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K
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TCAS resolution advisory, flight crew incorrectly climb or descend following the resolution advisory
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L
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An aircraft being provided with RVSM separation is not RVSM approved (e.g. flight plan indicating RVSM approval but aircraft not approved, ATC misinterpretation of flight plan)
Example 1: Original flight plan details submitted by FIR A for outbound leg showed
Aircraft 1 as negative RVSM. Subsequent flight plan submitted by FIR B showed Aircraft 1 as RVSM approved. FIR A controller checked with aircraft shortly after entering FIR A and pilot confirmed negative RVSM.
Example 2: Aircraft 2 cruising FL310 was handed off to the Sector X controller
who noticed the label of Aircraft 2 indicated RVSM approval. The Sector X
controller had controlled the aircraft the day before. It was then a non-RVSM
aircraft. The controller queried the status of Aircraft 2 with the pilot who advised
the aircraft was negative RVSM.
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M
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Other
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