THE SECRETS OF ENGINE RIGGING REVEALED
A new P&WC-produced video helps aircraft mechanics by breaking down engine rigging into simple, repeatable steps. Airtime spoke to the two men behind this handy PT6A resource to learn more.
THE IMPORTANCE OF WELL-RIGGED ENGINES
Jan Hawranke, Externals, Controls & Nacelles (ECN) Program Leader for PT6A engines, remembers exactly when he started to worry that the art of engine rigging was in danger of disappearing.
During the course of one year, an aircraft OEM sent back a dozen fuel control units that appeared to be faulty and couldn’t be matched to each other on a twin-engine aircraft. This was a significant concern, since engines must be rigged exactly the same way to perform in harmony.
Jan didn’t understand why the units were being returned, though, since they were in perfectly good condition. That’s when the “aha” moment hit him: the real issue was that the OEM’s mechanics didn’t have the information they needed to rig the fuel control units properly.
Rigging—the process of hooking up engines to an aircraft’s body—is an integral part of the engine’s installation process. It has to be done with the utmost care each time an engine is installed, Jan explained to Airtime.
On an aircraft with two engines, if both are not rigged exactly the same way, one might produce more power than the other. The pilot will then have to compensate by adjusting the power lever positions. It would be like driving a car with brakes that pull the car to one side, requiring the driver to turn the wheel to keep the vehicle straight.
Rigging information is available in aircraft maintenance manuals (AMMs), but it’s a complex process that cannot fully be captured in a written document or reviewed at a glance.
“There’s an art to good rigging,” says Jan. “A lot of it comes down to the mechanic’s feel and experience. The fuel control units being returned were a red flag to us that something was changing.”
A lot of the veteran mechanics who mastered rigging 20 or 30 years ago are retiring now. The know-how that existed years ago, the unwritten details that make for good rigging, are being lost. We realized it was important to pass that knowledge on to younger mechanics.
A VIDEO THAT MAKES MECHANICS’ WORK EASIER
While the airframer is ultimately responsible for providing rigging information, P&WC has always worked closely with OEMs to develop clear and thorough explanations. Indeed, two decades ago, Jan worked on a video designed to complement the information found in AMMs with tips on the rigging process.
For various reasons, he was never satisfied with the original video, which was now out of date anyway. He decided it was time for take two. Jan turned to a master of the rigging craft, P&WC veteran Rob Winchcomb, to star in a new rigging video.
You want both engines to behave the same way all the time, especially when landing, which is one of the most stressful moments of a flight. It’s a handling issue. Well-rigged engines make the pilot’s workload easier by ensuring that the response from each engine is identical whenever the levers are operated.
The pair spent two weeks in Australia with a local production crew to create the video. To make it as authentic and useful as possible, it features in-service PT6A-powered aircraft, generously made available by Australia’s Royal Flying Doctor Service.
The AMM remains the main document that needs to be consulted. The video is designed to complement the manual and illustrate the rigging process in a more dynamic way to help mechanics better understand what it is and how it works.
THE FUNDAMENTAL RULE OF RIGGING
The video provides detailed instructions on every aspect of rigging, such as the differences between fine and coarse adjustment of the serrated washer, or how to match the travel of propeller levers. As Rob emphasizes, no matter what action is being performed, the number-one rule of rigging remains the same: whatever you do physically to one engine, do exactly the same thing to the other one.
The engines need to provide equal torque in both forward and reverse operation, and the cockpit levers need to be well matched for the pilot’s sake, so once you’ve made the physical connections on each side, you should check that the levers are not staggered.
As mentioned in the video, it’s also a good idea to have two people in the cockpit when performing this complex job, with one operating the engine and the other following the instructions and writing down the results. The more efficient you are, the less fuel you will burn during the final checks in the engine run bay.
P&WC will eventually release two different versions of the video for two different fuel control unit models, starting with the first one below. Click on the links to watch:
Rigging your PT6A engines for King Air B200:
- Part 1: https://youtu.be/zPjGof4CcRc
- Part 2: https://youtu.be/sdC8ZQTwPWs
- Part 3: https://youtu.be/0VKkGcOGSYo
Rigging your PT6A engines for King Air B350:
I’m very proud that Rob and I have been able to put great content out there that will benefit the PT6A community by minimizing the rigging workload for aircraft mechanics.