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Recommendation issued to: AirServices Australia

Recommendation details
Output No: R19980002
Date issued: 13 January 1998
Safety action status:
Background:

SUBJECT

GPS Arrival - Wynyard (Tasmania)


BACKGROUND

A report was received by BASI through the "INDICATE" safety program [see note below] that aircraft equipped with Ground Proximity Warning Systems [GPWS] experience nuisance warnings on the approach to Wynyard [Tasmania] when using the GPS arrival procedure.

These warnings occur on the inbound track, from position CAMUS, of 158 degrees which takes aircraft directly over the steeply rising terrain of Table Cape. The rapid change in elevation from sea-level to 716 feet AMSL can result in a "Terrain Terrain" warning from the GPWS while aircraft are at or approaching the Minimum Descent Altitude [MDA] of 1000 feet with the altimeter set on actual QNH. In Instrument Meteorological Conditions the warning requires the crew to respond immediately by initiating an overshoot procedure [refer to attachment 1].

It is reported that this warning can occur even with aircraft in the landing configuration and at reduced airspeeds.


Note: The "INDICATE" safety program is a proactive system for monitoring airline safety performance.


SAFETY DEFICIENCY

The GPS arrival procedure for Wynyard [Tasmania] requires aircraft to track directly over Table Cape. This can result in nuisance GPWS warnings that either distract crews from their duties at a time of high workload or result in crews ignoring these warnings altogether.


ANALYSIS

In addition to the report through "INDICATE", another operator advised that GPWS equipped aircraft had experienced similar warnings when conducting the decommissioned Australian DME arrival procedure, which had a similar track and profile.

The safety value of GPWS is dependent upon the reaction of crew to any warning from the system. The standard response to a GPWS warning requires the crew to immediately initiate a climb. The existence of nuisance warnings will diminish the effectiveness of GPWS as it may result in crews ignoring warnings.

If the GPS Arrival track were displaced by 15 to 20 degrees to avoid directly overflying Table Cape, the terrain profile would not trigger unnecessary GPWS warnings.

Output text

BASI recommends that Airservices Australia modify the GPS Arrival procedure for Wynyard so that the track does not require aircraft to fly directly over the steeply rising terrain of Table Cape.

Initial response
Date issued: 03 February 1998
Response from: AirServices Australia
Action status: Closed - Accepted
Response text:

I refer to your letter R980002 (B97/131) dated 13 January 1998 and the recommendation contained therein, that the GPS Arrival procedure from position CAMUS to Wynyard be amended so that the inbound track does not require aircraft to fly directly over the steeply rising terrain of Table Cape.

Your proposal has been examined and indeed discussed with the operator concerned, and it is agreed that your proposal is the only viable option to overcome the GPWS alert problem on this instrument approach. Accordingly, this approach will be redesigned into a sector arrival thereby allowing GPWS equipped aircraft to track to the east of Table Cape, thereby overcoming the unnecessary GPWS warnings on this approach. The revised procedure will be published in DAP-E AL 63, which becomes effective on 26 May 1998. An advanced copy of the revised procedure will be made available to the CASA Melbourne District Office as soon as it becomes available and they have agreed to issue it to the affected operators for early implementation.

 
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Last update 01 April 2011