Type training · Boeing 737 Classic B1.1 · ATA 49

Boeing 737 Classic B1.1: GTCP85-129 APU (ATA 49)Type training questions & answers

The GTCP85-129 APU: start and speed switch logic, protective shutdowns, governor and thermostats, bleed and oil.

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Sample GTCP85-129 APU questions with answers

Three questions from the free preview. Think of your answer first, then open the explanation.

  1. 1.What compressor and turbine does the 737 Classic GTCP85-129 APU have?

    • A.Centrifugal compressor, radial turbine
    • B.An axial compressor with a two-spool turbine
    • C.A free power turbine with a load compressor
    Show answer and explanation

    Correct answer: A. Centrifugal compressor, radial turbine

    The GTCP85 has a two-stage centrifugal compressor (double-entry first impeller) and a radial turbine wheel. Ref 737-300/400/500 AMM 49-21-00 (GTCP85-129).

  2. 2.Which 737 Classic GTCP85-129 models use the electronic temperature control (ETC)?

    • A.Every GTCP85-129 model, all of them
    • B.Only the original model (A)
    • C.Models (H), (J) and (K)
    Show answer and explanation

    Correct answer: C. Models (H), (J) and (K)

    APUs with the ETC are GTCP85-129(H), (J) or (K); identify the model with the cowl open and lower shroud off. Ref 737-300/400/500 AMM 49-00-00 (GTCP85-129).

  3. 3.When the 737 Classic GTCP85 reaches 100%, what must be done if large bleed demand is needed?

    • A.Open the surge valve fully
    • B.Select a higher APU speed
    • C.Reduce the electrical load
    Show answer and explanation

    Correct answer: C. Reduce the electrical load

    Pneumatic and electrical power are available at 100%; if a large bleed load is needed, the electrical load must be decreased. Ref 737-300/400/500 AMM 49-00-00 (GTCP85-129).

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Part of the Boeing 737 Classic B1.1 type course

One chapter of the Boeing 737 Classic B1.1 type course question bank, for the 737-300/400/500 with CFM56-3 engines, written in our own words for revision. Your type course and the aircraft maintenance manual stay the authority: limits and procedures can differ between airframes and operators.

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