Aviation safety investigations & reports
Operational event - Agusta Westland AW139, VH-ESH, 89 km south-east of Townsville, Qld, 2 February 2009
AO-2009-004
Summary
On 2 February 2009, an Agusta Westland AW139 helicopter, registered VH-ESH, departed under the instrument flight rules from Mackay Aerodrome for Townsville Aerodrome, Queensland. The purpose of the flight was to return the helicopter to Townsville following the passage of a tropical cyclone.
Shortly after departure from Mackay, the crew were presented
with an increasing number of alert messages indicating the failure
of various helicopter systems. While the crew were focussed on
assessing these messages, the autopilot altitude hold function
disengaged, leading to a descent that was not detected by either
the flight crew or air traffic services (ATS).
The helicopter descended undetected for over 6 minutes while
flying towards an area of rising terrain, losing about 3,300 ft of
altitude, before ATS observed the descent and alerted the
crew.
The investigation determined that the helicopter sustained two
independent technical problems; one associated with water and
particulate ingress and a second related to the probable
susceptibility of the air data system to in-flight turbulence.
These failures resulted in multiple erroneous alert messages and
uncommanded disengagement of the altitude hold function. The
investigation also identified a number of safety factors relating
to workload and task management by the crew and monitoring of the
aircraft by ATS. That included the lack of an altitude deviation
alert within the Australian Defence Air Traffic System
(ADATS).
Following the occurrence, the helicopter manufacturer and
operator, and the Civil Aviation Safety Authority (CASA)
implemented a number of safety actions relating to the identified
technical and operational safety issues. In addition, the
manufacturer and operator of the helicopter, and CASA undertook
proactive safety action in a number of cases for which no safety
issues were identified.
A replacement common ATS system for ADATS and the civilian
Australian Advanced Air Traffic System (TAAATS) has been announced
by the Government that could be expected to include common alert
functions, such as the existing cleared level adherence monitoring
alert in TAAATS.
Safety Issues
Aircraft design permitted avionics malfunction via moisture
The design and relative positioning of the external air vent and avionics modules permitted the ingress of moisture and particulates that led to corrosion and contamination of electronic avionics components and consequently the generation of multiple erroneous crew alerting system (CAS) messages due to electrical shorting.
| Issue number: | AO-2009-004-SI-01 |
|---|---|
| Who it affects: | Operators of ‘long nose configuration’ AW139 helicopters |
| Status: | Adequately addressed |
Lack of formalised monitoring role
The lack of formalised procedures in place requiring the Air Crew Officer (ACO) to monitor key instrument indications probably contributed to the undetected altitude loss.
| Issue number: | AO-2009-004-SI-02 |
|---|---|
| Who it affects: | Helicopter operator |
| Status: | Adequately addressed |
Lack of deviation alert on ATC system
The absence of an altitude deviation alert within the Australian Defence Air Traffic System increases the risk of undetected altitude variation and contributed to the significant loss of altitude.
| Issue number: | AO-2009-004-SI-03 |
|---|---|
| Who it affects: | Operations receiving Air Traffic Services via the Australian Defence Air Traffic System |
| Status: | Adequately addressed |
Electrical interuption due to water ingress
Interruption of electrical power to the multi purpose flight recorder due to water ingress removed of an important source of information used to identify safety issues.
| Issue number: | AO-2009-004-SI-04 |
|---|---|
| Who it affects: | Operators of ‘long nose configuration’ AW139 helicopters |
| Status: | Adequately addressed |
General details
| Date: | 02 February 2009 | Investigation status: | Completed | ||
| Time: | 1030 EST | Investigation level: | Complex - click for an explanation of investigation levels | ||
| Location (show map): | 89 km south-east of Townsville Airport | ||||
| State: | Queensland | Occurrence type: | Warning devices | ||
| Release date: | 05 October 2010 | Occurrence category: | Serious Incident | ||
| Report status: | Final | Highest injury level: | None |
Aircraft details
| Aircraft manufacturer | Agusta, S.p.A, Construzioni Aeronautiche | |
|---|---|---|
| Aircraft model | AW139 | |
| Aircraft registration | VH-ESH | |
| Serial number | 31083 | |
| Type of operation | Aerial Work | |
| Damage to aircraft | Nil | |
| Departure point | Mackay Qld | |
| Destination | Townsville Qld |