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Engines

Overview

The Twin Otter comes with a pair of P&W PT6A turbine engines. The -100 variants sport 550 SHP PT6A-20, the -300 variants use PT6A-27, flat-rated to 620 SHP.

Custom engine simulation

At the heart of the mod sits a custom engine simulation that approximates the engine and many of its components. Built from scratch, it grew over time to a quite sophisticated model (I think). It is tuned to the POH performance charts and real-world reference data, and it is still work in progress, but already deeply integrated with many other aircraft systems.

Operation

If you're familiar with free-turbine engines, you will have no issues starting the engines using your normal procedure. If not, you should rely on the checklists. If you let the battery run out of juice, you can summon a GPU cart. In extreme cold, heating the engines using the "Pre-heat" feature on the Systems tab of the EFB app is recommended.

According to the POH, the correct point to introduce fuel is when Ng has stabilized above 12%. That means: let the needle settle, make sure it has settled above 12% Ng and then push the fuel levers forward. If the needles settles below 12% Ng, abort the procedure and charge the battery or use the GPU cart. The fuel levers are mechanical levers that open a fuel valve using cables and pulleys, there is no "low idle" and "high idle" or similar in the Twin Otter.

It's not possible to cross-start the engines. The generator of the running engine does not provide the current needed for the operation of the starter. To enforce this in the mod, the opposing generator is disconnected temporarily while the starter is cranking. You'll notice that the respective Generator annunciater will light up. The current pulled by the starter will make the lights in the aircraft dim or flicker.

The mod introduces subtle differences between the two engines that are randomly rolled (and persisted, if you opted in). For example, one of the engines might run slightly hotter than the other. (This is exposed in the EFB app as "Age Factor".)

Reviewed 2026-08-29.