The reporter has raised a safety concern in relation to increased workload and subsequent fatigue to flight crew as the result of continued deferred maintenance of an [aircraft] radio altimeter.
The reporter states, [Operator] [aircraft] [registration] has been operating for approximately the last 6 weeks with a First Officer's intermittent radio altimeter fault under minimum equipment list (MEL) [number] which has a B interval of 3 days to rectification. This MEL also then invokes MEL [number] auto-land system unserviceable. [Operator] has insufficient down time to rectify faults and engineers will clean a plug or swap a component from left to right and ground test okay before signing off the MEL. On the subsequent flight, the fault will then reappear and at the next port the MEL is reapplied for another 3 days, again and again.
The reporter states, the [Operator] fuel policy has been reduced from [xx] minutes to [x] minutes fixed fuel reserve. These aircraft operate mostly on ultra long-haul flights. The provision and use of auto-land is a mitigating factor for crew fatigue and the reporter provided the following example:
The flight crew of an aircraft recently conducted a go-around in [Location 1] as they were unable to do an auto-land after a [Location 2] to [Location 1] sector landing in the early morning with a problem with the approach lights.
The reporter provided a scenario whereby in the event that a flight passes the calculated point of no return and the weather at the destination deteriorates, the aircraft is not able to divert and is committed to land. This along with the combination of reduced final fuel reserve and no auto-land, is a huge threat to aviation safety.
The reporter further states, 'MELs were designed to allow scheduling of aircraft for rectifications depending on the severity of the fault. They were not designed to allow operators to manipulate the time interval allowed because they have a combination of insufficient spares, insufficient aircraft for down time or insufficient manpower to rectify'.
[Operator] would like to acknowledge the concerns raised by the reporter in relation to radio altimeter (RA) faults on [registration].
[Operator] engineering has reviewed the maintenance history for [registration 1] and can confirm a history of RA defects that have resulted in MEL [number] being applied to the RA system on this aircraft four times since [date]. Each time the MEL was applied, maintenance action was performed prior to the MEL being cleared. To date the maintenance action has included replacement of antennas and transceivers in the RA system. Following the most recent reported event on [date], the transmit and receive antennas were replaced and there have been no subsequent reports of RA defects.
The RA system on the worldwide [aircraft] fleet is the subject of an ongoing reliability improvement program. [Operator] continues to work with [Manufacturer] on addressing anomalous faults with this system that can be transient and result in the RA entering a 'no computed data' (NCD) state, and/or presenting a transient fail warning condition which could cause a 'NO AUTOLAND' engine indicating and crew alerting system (EICAS) message. These anomalous messages often self-clear and are not active post flight or are able to be cleared using the testing procedures provided by the aircraft’s Fault Isolation Manual (FIM) or Aircraft Maintenance Manual (AMM). [Operator] has confirmed with [Manufacturer] that these events are not related to 5G interference.
[Manufacturer] have developed an engineering modification program to improve the RA system reliability which involves the replacement of the transmission line components (coaxial cable and antennas) that may degrade in service and due to signal attenuation lead to the NCD RA readings. [Manufacturer] have provided [Operator] with six shipsets of transmission line components for replacement on [registration 2] to [registration 1], with [registration 2] the first aircraft to have these components replaced last week, and [registration 1] to be modified on [date]. Further to this, [Manufacturer] is also looking to introduce a larger coaxial cable modification to the system to reduce signal attenuation risks and this is expected to be approved in late 2024.
Regarding the reporter’s arrival fuel scenario, all flights are operated in accordance with the airline's approved fuel policy. The fuel policy takes into account forecast weather conditions at the destination airport in determining the required amount of fuel. The airline's data monitoring program monitors arrival fuel on a port by port and fleet by fleet basis, this data is used to adjust fleet specific fuel policy elements, as well as airport arrival allowances.
[Operator] thanks the reporter for raising their concerns regarding RA faults on [registration 1] and would like to reassure the reporter that [Operator] continues to work with [Manufacturer] to understand and rectify the issue.
The [Operator] fatigue risk management system (FRMS) fatigue risk predictive processes should identify high workload due to permissible unserviceability’s (PU) (combined if more than one) during the last approach and landing.
In relation to the auto-land system being a mitigator for ultra-long haul crew fatigue, CASA considers that the [Operator] FRMS should appropriately take into account reports regarding repeated maintenance issues that may impact on aircraft safety at the end of long-haul flights.
To operate without the radio altimeter passed the prescribed MEL time limit can only be done as a once off extension. Making it 6 days would require a PU to have been issued and CASA has no record on one being presented to the Airworthiness Engineering Branch for process. It is likely that [Operator] may have issued the PU for their aircraft. Based on [Operator]’s response the radio altimeter issue was rectified each time. Therefore, it was not a continuous use of MEL for 6 weeks.
In relation to the fuel reserve matter raised by the REPCON correspondent, CASA considers that the [Operator] approved fuel policy is acceptably safe during a known transition period to operations being conducted under the CASR Part 121 rules.