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Mode Aviation
Reference No. AR201400061
Date reported 23 July 2014
Concern title Confusion in the cockpit when given an instruction to descend while flying the Sydney / Bankstown WATTLE FIVE STAR
Concern summary

The concern related to the confusion in the cockpit when ATC instruct the crew to descend when flying the WATTLE FIVE STAR.

Industry / Operation affected Aviation: General aviation
Concern subject type Aviation: Policies & Procedures

Reporter's concern

The reporter expressed a safety concern in regards to when ATC issue the clearance to descend when flying the Sydney / Bankstown WATTLE FIVE STAR [standard arrival route].

The reporter advised that they are regularly advised to ‘leave controlled area on descent’ before they reach the 20 DME limit. This is the point where ATC should be issuing a descent, as described in the published procedure. This leaves pilots unsure of what is expected of them as the LSALT [lowest safety altitude] is 4700 ft and the lowest level of controlled airspace is 4,500 ft.

The controller does not check if the aircraft is visual before the descent clearance is issued.

Reporter comment: There is potential for an unfamiliar (or low time) pilot to just start a descent in this situation without having any assigned level to descend to.  This occurs right over the high terrain of the Blue Mountains, with possible disastrous consequences.

Operator's response (Operator 1)

Airservices Australia (Airservices) appreciates the opportunity to respond to the reported concern regarding the issue of clearances by ATC to descend when flying the Sydney / Bankstown (SY / BK) WATLE FIVE standard arrival route (STAR).

Airservices would like to provide the following clarifications to assist with the interpretation regarding how the WATLE FIVE procedure should be flown.

Airservices clarifies that aircraft approaching an aerodrome must not descend below the lowest safe altitude (LSALT) for the route segment being flown, or the published minimum sector altitude (MSA) in accordance with paragraph 1.4 of the Aeronautical Publication (AIP) - ENR 1.5.

With reference to the reporter's statement that they were advised by ATC to ‘leave controlled area on descent’, Airservices confirms that the LSALT for the WATLE FIVE route is 4700 FT.

However, MSAs are available for lower descent indicated on the WATLE FIVE STAR procedure as the following:

  • At 25 NM BK (34 DME SY}, the MSA is 3700 FT
  • At 15 NM BK (24 DME SY), the MSA is 2500 FT.

Following the receipt of the ATC instruction, aircraft are required to descend in accordance with the MSA which was designed to ensure aircraft remain clear of terrain and below Class C steps.

Airservices notes that the WATLE FIVE STAR procedure will be cancelled on 13 November 2014 when the Sydney VOR is decommissioned. An alternative route will be published featuring a LSALT of 2000 FT at 21 DME Sydney (refer to Attachment 1 for more information).

Regulator's response (Regulator 1)

CASA has reviewed the concerns raised in the REPCON and wishes to advise that the WATLE FIVE STAR has been withdrawn.

ATSB comment

In response to these responses the reporter advised the following:

Thanks for the response, and I note the WATLE FIVE STAR has been withdrawn.

I do have a further comment in relation to the response from Airservices, and this should be relevant for any further approach designs:

Airservices states: ‘Following the receipt of the ATC instruction, aircraft are required to descend in accordance with the MSA which was designed to ensure aircraft remain clear of terrain and below Class C steps.’  This is not stated on the approach plate.  It is only ‘assumed’ the pilot is to interpret the MSAs for that purpose.  Anyone who has flown would design an approach to be clear, unambiguous and not open to interpretation.

The 25nm and 15nm BK MSAs listed on the WATLE FIVE chart are not a part of the approach.  Nowhere in the STAR text did it refer to those MSAs.  It is not acceptable for ATC to expect a pilot to have to ‘interpret’ anything other than what is stated in the approach.

If the STAR was to require a pilot to use those MSAs then I would have thought it prudent for Airservices to explicitly state that in the approach, rather than expecting the pilot to ‘work out’ what was expected.

For example - the STAR text could have easily said something along the lines of ‘If cleared to leave CTA on descent to YSBK then at 34DME SY (25nm BK) descend to 3700 ft and then at 24DME SY (15nm BK) descend to 2500 ft.  If not visual at 2500 ft then conduct ….’.

I don’t think it is very smart approach design to expect pilots to have to work beyond the specific text that is listed on the approach.  Workloads are high in bad weather and basic human factors considerations would preclude any such approach designs.

While local pilots were aware of these ‘expectations’ my concern is all about pilots unfamiliar with the airspace being given a confusing and ambiguous clearance without guidelines from the approach plate.  I recently flew with a pilot not from the Sydney area (he had 15000+ hours flying experience, mix of airline and GA) and he had absolutely no idea what ATC were expecting him to do when they gave this clearance.  It is not theoretical - people were genuinely confused as to the expectations.

Thanks for following this up.  I would like the think Airservices will be more practical in their approach design in future to consider the workloads that pilots (particularly in single pilot operations) are under in situations of bad weather where these approaches/STARs are critical.

Airservices provided the following response in relation to these comments:

Airservices notes the CASA response and confirms that the WATLE FIVE procedure has been withdrawn, effective 19 August 2014.

Furthermore, Airservices appreciates the additional feedback provided by the reporter which been provided to Airservices instrument flight procedures design team for reference.

 

Attachment 1: New route structure on VTC

 
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Last update 15 May 2015