Taking a team approach to evaluating engine performance
Setting the stage
Addressing customer concerns about performance margins
In late 2018, Mack Air -- a Botswana-based tour and shuttle operator -- noticed that some PT6A-140 engines in its fleet of Cessna Grand Caravan EX aircraft were losing temperature margins. The interstage turbine temperature (ITT) margin had reduced at a rate faster than expected, given that the aircraft were only around 12 months old.
Concerned about the potential long-term impact on engine performance, Mack Air reached out to Pratt & Whitney for support. That set in motion a joint, multi-pronged investigation that ultimately helped the customer gain a better understanding of the new engine’s operating and maintenance requirements.
FAST™ data plays key role
The Pratt & Whitney support team reviewed data collected using the Pratt & Whitney FAST™ technology. This engine health trend monitoring system, which is installed on all of Mack Air’s fleet, captures and wirelessly transmits full-flight data for analysis within minutes of the pilot shutting down the engine.
As Francis notes, the data was a valuable resource during the investigation process.
One of the first things we did before sending engines to the test cell, is review the FAST™ data on these engines to confirm Mack Air’s reports. Not only did we confirm that the rate of deterioration was higher than expected, we were also able to see that all the pilots were operating the aircraft consistently and exactly as they were trained to do. We were therefore able to make some recommendations. For Pratt & Whitney, this investigation would have been much more difficult without this data.
Based on the review of our FAST™ data, Pratt & Whitney confirmed that all pilots were operating the aircraft in a consistent manner, reinforcing that our training program was effective. It was rewarding for our team to hear that from the manufacturer and it gave me confidence that my team would implement the changes suggested by Pratt & Whitney.
A best practice to minimize compressor erosion
However, due to the nature of its design, the inertial separator needs the forward motion of the aircraft to be effective.
We discovered through an exhaustive study that while the aircraft was parked in certain environments with the engine running at low power, foreign debris was sucked into the engine with air through the intake door on the side of the aircraft. This was having an adverse impact on the compressor.
Mack Air’s business involves keeping engines running during short stops in between flights on unpaved runways in a dry, dusty environment. This was a major contributing factor to the situation.
Adjusting maintenance practices for a new engine model
Every engine model is different. You cannot always apply the same maintenance practices even if they look similar externally, because on the inside they could be completely different and may require different maintenance intervals.
Benefits of a global network
“Since the customer is located in Botswana and already had a working relationship with StandardAero, our Designated Overhaul Facility in South Africa which has significant experience with this engine model, it was only logical to ask them to inspect some of the engines and they did a great job,” explains Francis. “Mack Air’s peak season was approaching, so we doubled down on the investigation process by leveraging the Pratt & Whitney Engine Services (P&WES) shop in West Virginia, which also has considerable experience with in-service PT6A engines. Also assisting throughout the whole investigation was the Pratt & Whitney MRO Engineering organization – namely Louis Simoneau – whose insights were invaluable. Only the shops in our Global Service Network have access to our in-house experts like Louis, that’s often a determining factor in identifying an issue quickly and resolving it once and for all.”
The expertise of these facilities, combined with Pratt & Whitney’s strong working relationship with both the customer and the Cessna Caravan’s manufacturer, Textron Aviation, helped to isolate the cause and reverse the ITT performance deterioration to Mack Air’s satisfaction.
The cooperation between Mack Air, our maintenance provider Absolute Aviation Botswana, StandardAero, P&WES, Textron Aviation and Pratt & Whitney was amazing. It’s was a perfect example of good customer support and a strong support network.