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Descent mode management and Flight Control Unit altitude selection

Issue number: AO-2012-103-SI-01
Who it affects: All operators of highly-automated aircraft
Issue owner: Jetstar Airways
Operation affected: Aviation: Air transport
Background: Investigation Report AO-2012-103
Date: 13 March 2014

Safety issue description

The operator’s procedures did not require the flight crew to specifically check the active auto-flight mode during descent, and allowed the crew to select the Vertical Intercept Point altitude when cleared for the approach by air traffic control. This combination of procedures provided limited protection against descent through an instrument approach procedure’s segment minimum safe altitudes.

Proactive Action

Action organisation: Jetstar Airways
Action number: AO-2012-103-NSA-32
Date: 13 March 2014
Action status: Closed

On 22 January 2014, Jetstar stated that the application of the Airbus Golden Rules was embedded in its operation and was regularly emphasised throughout pilot training sequences and should be applied during all operations. It also advised that, in January 2013, the discussion of Operational Golden Rules in its Flight Crew Training Manual was significantly expanded (consistent with changes to the Airbus manual). This additional text included the following:

Understand the FMA at all times.

The flight crew must confirm the operational effect of all actions on the FCU, or on the MCDU, via a crosscheck of the corresponding annunciation or data on the PFD and on the ND.

At all times, the flight crew should be aware of the following:

  • Guidance modes (armed or engaged)
  • Guidance targets
  • Aircraft response in terms of attitude, speed, and trajectory
  • Transition or reversion modes.

Therefore, to ensure correct situational awareness, at all times, the flight crew must:

  • Monitor the FMA
  • Announce the FMA
  • Confirm the FMA
  • Understand the FMA.

Jetstar also advised that, on 15 November 2012, a specific warning was included on its Queenstown approach chart to state that:

In normal circumstances, managed descent mode is required beyond the IAF.

Jetstar also stated:

With respect to this particular incident it is apparent that the crew did not apply the Airbus Golden Rules nor did they follow the recommendation documented in our Route Manual Supplement Queenstown section as per below:

“Approach charts specify minimum segment altitudes prior to the VIP. Managed descent mode provides protection against infringing these minimum altitudes. If selected vertical modes are used, pilots must exercise caution in complying with these altitudes. It is strongly recommended that pilots use managed descent mode in preference to selected vertical modes, especially when re-intercepting the vertical path from above prior to the VIP.”

With the above in mind, Jetstar believes that there is no specific requirement to check the active mode during descent. The pilots should have been fully aware of what vertical mode the aircraft was in without verbalising it. Jetstar also assert that had the above recommendation been followed, the crew would not have been in a selected descent mode during descent.

ATSB response:

The ATSB notes that Jetstar has provided additional guidance material regarding auto-flight mode awareness in its flight crew guidance material. It also notes that specifically mandating the requirement for crews to select the managed descent mode prior to the initial approach fix on the Queenstown approach charts will potentially reduce the likelihood that crews will not be in that mode by that point, although it is noted that the flight crew of the occurrence flight on 16 July 2012 were actually intending to change to managed descent mode prior to this point.

The ATSB acknowledges the difficulty of further minimising the likelihood of these rare types of monitoring errors, and that there are effective risk controls in place to prevent such monitoring errors from resulting in a more serious occurrence.

 

Additional safety action by Jetstar Airways

In response to this occurrence and in the context of the results from its line audits, Jetstar advised that it reviewed its sterile flight deck policy as part of a broader review of operational distractions. As a result of that review, the period during descent where the sterile procedures apply will be condensed ‘to support a greater level of discipline’.

   
Current issue status: Partially addressed
Status justification:

The ATSB is satisfied that the safety action will reduce the risk of the safety issue to some extent.

 
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Last update 13 March 2014