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First Air’s ATR42 combi page 7

Story and photos by Raymon J. Kaduck

The Pratt and Whitney Canada PW 120 turboprop engines provide 1,800 shaft horsepower of takeoff power, which can be pushed to 2,000 with an engine out. The engines are “free turbines” and the reduction gearbox can be locked with a propeller brake without affecting the low and high pressure spools of the engine. Using the running engine instead of an additional APU saves weight, initial cost and maintenance time. Engine life is not affected when the engine is run at ground idle, which is sufficient to provide full electrical power.

With its prop braked and the engine in “hotel mode,” the passengers can remain on board while the aircraft is fueled, shortening station stops. Pilot James Johnston says that the use of the engine as an APU occasionally calls for some precision manoeuvring prior to fueling: “You have to get close to the pump, but also want to keep the fueling side close into the wind so that exhaust stays out of the cabin air. On the other hand, with this aircraft, a pilot can pull directly into the pumps and back out again.”

Although it is possible to fuel the aircraft using gravity feed from the top of the wing, First Air uses underwing pressure fueling exclusively. Generally, northern communities already have pressure fueling equipment, according to Chief Pilot Bill Roach.

Some concerns have been expressed about the location of the refueling panel on the right landing gear fairing; however, the fuel controls have to be on the side of the aircraft that is fueled, and the left engine has to be stopped because that is the side that passengers and freight are loaded from. The control panel is located behind the propeller arc. One national fuel distributor refuses to refuel the aircraft with the engine running.

“Although the aircraft is certified in this configuration for fueling, some refuelers have taken the stand that, despite the fact that the propeller is stopped, the engine is running, so it is hot refueling,” says Orr. “The Transport Canada certification of the aircraft says that when the engine is in hotel mode, it is an APU. This is something we had not anticipated.”

The aircraft develops 28V (400A) DC power using starter/generator units driven through the auxiliary gearbox of each engine. Constant frequency AC is supplied through the DC system by two static inverters rated at 500VA.

Two independent hydraulic systems (blue and green) operate simultaneously at all altitudes and temperatures. Each has its own AC electric pump delivering 3,000 psi. The blue system also has an auxiliary 28V DC electric pump, which is used to provide power while the aircraft is on the ramp. The hydraulic system is designed in modular form and can be accessed from the left gear fairing behind the wheels.

Pneumatic de-icing boots are built into the leading edges of the wings and tailplane. Electrical heat is supplied to the propellers, windshields, pitot and static probes and the horns [tips] of the ailerons and rudder.

The tricycle landing gear has been engineered for smoothness and stability. The main gear has a trailing-type design for smoother landings and the doors are mechanically linked to the gear. The aircraft is fitted with an anti-skid system and disk brakes. Commonality is also an important design criteria. Virtually all of the main gear components, except the shock struts, are interchangeable between right and left sides.

The aircraft design uses composite materials for 14% of its total structure. The composite parts are impervious to cracks and corrosion and provide superior strength with less weight. This improves payload and reduces fuel burn. Kevlar/Nomex sandwich material is used for cabin floors, leading edges, wheel fairings and some engine fairings. Carbon/Nomex is used in the engine cowlings, flaps and elevators. A carbon monolithic structure is used for the majority of the rudder and horizontal stabilizer surfaces, as well as the ailerons. The manufacturer claims the weight saving is a significant 190 kg, or the equivalent of two passengers.

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maintaining the ATR
by Raymon J. Kaduck

First Air ATR42 at Carp, ON

Click on the photo to read a detailed report. © 2011. All Rights Reserved