19POS08 DOWNLINK OF PILOT SELECTED LEVELS

Position 19POS08 22 August 2019

Downlink of pilot selected levels

BACKGROUND

For some time now, several ATS Units (ATSUs) have been using an alert function that is based on data sent by the Enhanced Mode S transponder. This transponder version provides a down-link of various airborne parameters that includes the flight level or altitude selected by the pilots in the altitude window of the associated auto-flight system.

If the pilot selected flight level or altitude does not correspond with the cleared level/altitude stored by the controller in the ATM (Air Traffic Management) system, an alert is triggered at the controller station. This warning is used by the controller to verify the pilot selected level/altitude and provides a valuable safety net.

According to ICAO procedures described in ICAO Doc 4444, 4.5.7.5, a voice-readback (or alternatively, confirmation by CPDLC) of all cleared levels/altitudes is always required. The display of a selected level/altitude at the controller working position may not be used as a substitute, but only for information.

Due to varying aircraft designs and airlines’ standard operating procedures, pilots may sometimes select intermediate levels/altitudes on SIDs and STARs, whilst they have been cleared for an even higher/lower level/altitude. Even though the crews understand the clearance and are adhering to it, their selection may trigger an alert at the controller working position. The controller then has to check the cleared level/altitude causing unnecessary frequency congestion. In the past, this has led to confusion, frustration, and even discussions on the frequency. This is a nuisance for other airspace users and a possible safety hazard during a critical phase of the flight.

POSITION

IFALPA endorses the above ICAO provisions, but stresses that:

• Downlinked selected levels should not be used for clearance readback and should not replace a voice-readback or CPDLC clearance confirmation.
• Controller alerts should not be removed as they are a valuable safety net, even though they sometimes create ‘nuisance’ alerts.
• Selecting an intermediate level different to that which has been cleared (for example, ‘climb/descend via’ SIDs/STARs) may lead to an alert at the ATSU, and related ATC queries.

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