Aviation occurrence briefs

Unforecast weather involving Boeing 717, at Canberra, ACT, on 2 November 2018

Number:
AB-2018-123
Status: Completed
Investigation completed

Brief

Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation.

What happened

On 2 November 2018 at approximately 1400 Eastern Standard Time (0400 UTC), the crew of a Boeing 717 at Brisbane, Queensland obtained a weather brief on their destination airport, Canberra, Australian Capital Territory.

The weather brief obtained included a TAF[1] for Canberra aerodrome and the latest TTF[2] SPECI[3].

Table 1: MET products obtained by crew

TAF

TAF AMD YSCB 012302Z 0123/0224 32020G35K 9999 -SHRA SCT050

BECMG 0206/0208 32013KT 9999 -SHRA SCT050

FM021500 29014KT 9999 FEW050

BECMG 0222/0224 28015G25KT CAVOK

PROB30 INTER 0204/0209 VRB30G45KT 5000 TSRA SCT020 SCT060CB=

TTF

TTF SPECI YSCB 020330Z 33025G40KT 9999 FEW050 BKN100 31/06 Q1012

RMK RF00.0/000.0

FM0330 MOD/SEV TURB BLW 5000FT

 

The TAF published at 2302 UTC on 01 November 2018 and valid between 0400 and 0900 UTC on 02 November 2018 had a PROB 30 INTER for thunderstorms, which indicated a 30% probability of thunderstorms occurring. The TTF SPECI published at 0330 UTC and valid for 30 minutes after the crew’s scheduled arrival time at 0400 UTC did not include thunderstorms. No TTF SPECI published up to 0600 UTC on that day included thunderstorm.

The crew additionally checked the Bureau of Meteorology’s (BOM) weather radar which confirmed a weather system similar to that of a squall line approaching the Canberra region.

Based on the information published, the crew were inclined to believe that thunderstorms were not prevalent at Canberra, as information published in Aeronautical Information Package (AIP) GEN 3.6.3 states that the “TTF supersedes the TAF for its validly period and is the current forecast for pilots of aircraft whose arrival time falls within the validity period. It should be noted that PROB is not used in TTF (but is included in TAF).”

The aircraft was subsequently required to hold for 35 minutes before landing at Canberra, as the airport was closed due to thunderstorm activity.

Table 2: Timeline of events

Time (UTC)

Event

0359

Weather briefing obtained by crew – included TAF and TTF

0330–0553

TTF between periods 0330 to 0553 include strong wind gusts (up to 40 knots)

0405–0420

Aircraft departs Brisbane

0553

TTF from 0553 shows easing wind conditions (8 knots)

0600

Scheduled time of arrival

0640

Actual arrival time

 

Figure 1: Geographical Area Forecast (GAF) with highlighted contact details

Geographical Area Forecast (GAF) with highlighted contact details

Safety message

Crew are encouraged to seek further advice if they are in receipt of conflicting meteorological information or have any doubts regarding the accuracy of the published forecasts. Contact details are located at the bottom of the Geographical Area Forecast (Figure 1), which directs pilots to a forecaster for the area.

Whilst it is important to obtain specific information relating to the planned departure and arrival port, it is also important to have a complete picture of the area meteorological conditions to avoid unexpected conditions. Pilots are encouraged to use the wide range of meteorological information available.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

 

__________

  1. Terminal aerodrome forecast (TAF) is a format for reporting weather forecast information, particularly as it relates to aviation.
  2. The trend forecast is an aerodrome weather report to which a statement of trend, for the elements wind, visibility, weather and clouds, is appended, forecasting the weather conditions expected to affect the aerodrome for the validity period of the TTF which is normally the three hours following the time of the report.
  3. SPECI is special weather report issued when there is significant deterioration or improvement in airport weather conditions, such as significant changes of surface winds, visibility, cloud base height and occurrence of severe weather.
General details
Date: 02 November 2018   Investigation status: Completed  
Time: 1400 EST    
Location   (show map): Canberra    
State: Australian Capital Territory    
Release Date: 29 April 2019   Occurrence category: Incident  
Report status: Final    

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 717  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Nil  
Departure point Brisbane, Qld  
Destination Canberra, ACT  
Last update 29 April 2019