Windshear warning systems

Coulson Aviation fleet of C-130 aircraft were not fitted with a windshear detection system, which increased the risk of a windshear encounter and/or delayed response to a windshear encounter during low level operations.

Coulson Aviation consider a windshear detection system would not be effective for aerial firefighting operations and is not necessary as procedures, practices and training for the crews reduce the resultant risk to as low as reasonably practicable. The ATSB notes that Coulson Aviation has also advised it is not aware of a commercially available system that can be retrofitted to the C-130H aircraft in their specific configuration.

Response by Coulson Aviation
On 10 July 2022, in response to the draft report and identified safety issue, Coulson Aviation advised the ATSB that:
The reactive based system relies on aircraft performance instruments, combined with altitude, angle of attack, and accelerometer inputs. The reactive based systems alert the pilots of a windshear event once the airplane has entered the windshear event. The report quotes the FAA saying, “even reactive systems provide a valuable service in the detection, timely annunciation and confirmation of a potentially hazardous windshear condition generally in
advance of human pilot recognition time.” This type of system is of marginal value as it is of most utility when alerting a crew who are unaware of actual or impending windshear conditions. LAT crews knowingly operate within areas in which the precursor indications of windshear are expected and trained for.

We would make the point that given Coulson pilots’ experience in the firefighting environment that is often flown in unstable air, the aircrew are highly experienced in recognizing windshear type events and that their reaction time would be as timely, if not quicker, than a reactive based system.

The commentary on the use of a Predictive Windshear Detection equipment is flawed in a fundamental way. The Draft Report discusses the advent and development of this equipment that can give a flight crew a 5-10 second advance warning of a windshear event. These systems “used doppler weather radar and the moisture in the atmosphere to collect wind velocity data. Therefore, drier air would reduce the reflectivity and windshear warning time.”
Coulson is not aware of any system that could predict windshear in such a dry environment. Aerial firefighting takes place in a very dry environment that is conducive to active fires. With minimal or no moisture present in the atmosphere it can be concluded that the forward-looking Predictive Windshear Detection equipment would provide little or no advance warning of a windshear event.

Unless evidence that Predictive Windshear Detection equipment would provide detection in an extremely dry atmosphere (found around fires) can be provided, any discussion regarding Predictive Windshear Detection equipment for these types of operations, is irrelevant. As per various points made above, aerial firefighting operations knowingly fly into areas where windshear is prevalent. The procedures, practices and training for the crews reduce the resultant risk to as low as reasonably practicable.

ATSB comment
The ATSB acknowledges that forward-looking (predictive) windshear warning systems may have reduced effectiveness in drier environments. However, on the day of the accident, the windshear system on the Boeing 737 (whether predictive or reactive) activated when operating in similar environmental conditions to that very likely experienced by N134CG. Further, the fitment of a windshear system in the Lockheed Martin ‘FireHerc’, and acknowledgement by some of the pilots interviewed that they have had a positive effect on managing a windshear encounter, would suggest that these systems have a degree of effectiveness.

In the absence of an airborne detection system, a successful recovery from a windshear encounter is reliant on the pilot’s timely recognition and response, which research has shown could take 5 to 15 seconds. When conducting firefighting operations in the low-level environment, there is often limited time and height available for such recognition and response. Therefore, the ATSB believes that the fitment of windshear detection systems to the C-130 aircraft would be an important safety enhancement for aerial firefighting operations. As such, the ATSB issues the following safety recommendation to Coulson Aviation to take further action to address this safety issue.