Invisible agent behind deadly Sydney sightseeing air crash

The weather was fine and conditions were good on New Year’s Eve 2017, when a sightseeing plane took to the air over Sydney Harbour with a highly experienced pilot and five British tourists aboard – only to crash into the sea in circumstances so mysterious, the most likely explanation has only just surfaced.

Sydneysiders learned of the tragedy on the first day of 2018. The crash had killed acclaimed British chief executive Richard Cousins, his two sons, his fiancée and her 11-year-old daughter, and pilot Gareth Morgan. Morgan, 44, was a skilled pilot who specialised in seaplane aviation and Cousins was chief executive of the world’s largest food-service company, the Compass Group.

The plane was still climbing out of the Cottage Bay area when it suddenly banked 80 to 90 degrees to the right before diving into 13-metre-deep waters. The manoeuvre was described as inexplicable. Nobody could work out why the plane crashed about halfway down Jerusalem Bay, which is surrounded by steep terrain, has no exit and was not an authorised route, or one that the pilot had ever taken before.

Now, the Australian Transport Safety Board (ATSB) may have found the answer.

Silent, invisible and deadly carbon monoxide (CO) gas could be the culprit. The ATSB considers the high levels of CO detected in blood samples of the aircraft occupants “were likely to have adversely affected the pilot’s ability to control the aircraft during the flight”. The ASTB considers it is most likely that the pilot and passengers were exposed to CO inside the aircraft cabin.

The ATSB issued the following update to its investigation last week:

During the draft investigation report review process, the aviation medical specialist engaged by the ATSB recommended that carbon monoxide (CO) toxicology testing be undertaken on blood samples of the aircraft occupants that had been taken and suitably stored by the New South Wales State Coroner. This required testing at a specialised laboratory. With results pending, the ATSB draft report was submitted to Directly Involved Parties (DIPs) in December 2019 for comment.

The results of the testing were provided to the ATSB in March 2020, indicating that the pilot and two of the passengers had elevated levels of CO. The ATSB notes that post-mortem examinations established that the pilot and passengers received fatal injuries sustained as a result of the impact sequence.

Recovery of the aircraft wreckage from Jerusalem Bay. Source: ATSB

Since receiving the toxicology results, the ATSB has:

• consulted with New South Wales Health pathology to confirm the integrity of the samples given the preservation method, storage temperature and duration
• consulted with NSW Health forensic toxicology to confirm the accuracy of testing given the technique used and sample preparation
• received independent advice from a forensic pharmacologist, and engaged an experienced independent forensic pathologist to advise on the testing and effects of the CO levels found in the occupants
• undertaken research on CO poisoning and detectors relating to aircraft operations.

From this, the ATSB considers the levels of CO detected were likely to have adversely affected the pilot’s ability to control the aircraft during the flight.

Having discounted other potential sources of CO exposure, the ATSB considers it likely that the pilot and passengers were exposed to CO inside the aircraft cabin. To identify the source of CO in the aircraft cabin, the ATSB has:

• conducted a further examination of the aircraft, in particular, the exhaust system and engine firewall, and identified a potential source of CO and path for exhaust gases to enter the aircraft cabin
• reviewed the aircraft’s maintenance records for scheduled/unscheduled maintenance and inspections carried out on relevant components
• attended the maintenance facility to examine an exemplar exhaust system in-situ, and to discuss relevant maintenance procedures
• undertaken ground testing on an exemplar DHC-2 aircraft to replicate the potential source of CO and ingress into the cabin
• consulted with the Civil Aviation Safety Authority regarding the release of an airworthiness bulletin providing advice on CO issues.

From the above activities, the ATSB found pre‑existing cracking of the engine exhaust collector-ring, which could lead to exhaust leakage into the engine bay. Further, the ATSB found a breach in the firewall from missing bolts used to secure magneto access panels in the firewall under the instrument panel in the cabin. Any breach in the firewall can allow the ingress of gases from the engine bay into the cabin.

In order to communicate the significance of the above to the aviation industry, the ATSB has released the following two safety advisory notices, which:

• Remind aircraft maintainers of the importance of conducting thorough inspections of exhaust systems and firewalls, with consideration for potential CO exposure (AO-2017-118-SAN-001).
• Strongly encourage operators, owners and pilots of piston-engine aircraft to install or carry a carbon monoxide detector with an active warning to alert pilots of elevated levels of CO in the cabin (AO-2017-118-SAN-002).

Cottage Point area, standard flight path and accident location. Source: Google earth, modified by the ATSB

The ATSB is currently documenting the results of the additional work and developing findings for inclusion in the investigation report. The revised draft investigation report will be provided to Directly Involved Parties for a consultation period to provide an opportunity for them to consider and comment on the new information. Following completion of that review, it is anticipated that the final report will be released publicly on the ATSB website during Q3 in 2020.

The ATSB noted that the information contained in its web update was released in accordance with section 25 of the Transport Safety Investigation Act 2003 and is derived from the initial investigation of the occurrence. Readers are cautioned that new evidence will become available as the investigation progresses that will enhance the ATSB’s understanding of the accident as outlined in this web update. As such, no analysis or findings are included in this update.

For more, see the ATSB site here.

Written by Peter Needham