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Top 10 Must-Know Boeing 787 Engine Q & A

Posted23/07/2025
Updated23/07/2025
By SkyhighTEXsuperaps

The Boeing 787’s engines are modern marvels—quiet, powerful, and just a bit too smart for their own good 🧠✈️. But let’s be honest: unless you’re best friends with N1, N2, and N3, trying to understand the engine systems can feel like decoding a foreign language full of valves, acronyms, and surprise EICAS messages ⚙️🔍. Don’t worry—we’ve got you covered! This Q&A breaks down the key concepts in plain language—with a few laughs along the way 😂. Whether you’re sim prepping, geeking out, or just tired of nodding and pretending you know what the EEC actually does, this guide is for you 🛫📘.

1. What engines power the Boeing 787, and what’s their thrust rating?

🛠️ The Boeing 787 can be powered by two different engine types, depending on the airline’s configuration:

  • Rolls‑Royce Trent 1000 (commonly the D, TEN variants)
  • General Electric GEnx‑1B

Both engines are high-bypass turbofans designed for long-haul efficiency, fuel savings, and low noise.

  • The Trent 1000 delivers up to 76,000 lb of thrust, with most models rated around 70,000–74,000 lb.
  • The GEnx‑1B offers a similar thrust range, up to 76,100 lb, depending on the variant.

Although they differ in internal architecture and engine logic, both are fully interchangeable from a certification standpoint—though not physically interchangeable on the same aircraft. Operators choose based on performance goals, maintenance programs, and existing fleet commonality.

2. Explain the three-shaft core architecture: N1, N2, and N3.

  • N1: Fan and low-pressure (LP) turbine on a common shaft.
  • N2: Intermediate-pressure (IP) rotor, connected to the accessory gearbox.
  • N3: High-pressure (HP) compressor and turbine on their own shaft.
    This design enhances spool independence, performance, and response.
boeing engine

3. How does the 787 engine deliver fuel from tanks to the engine?

  1. Spar Fuel Valve in the main tank opens.
  2. First-stage pump adds pressure.
  3. Fuel passes first-stage filter.
  4. Second-stage pump significantly boosts pressure.
  5. Fuel Metering Unit (FMU), controlled by the EEC, regulates flow.
  6. Goes through second-stage filter, then
  7. Engine Fuel Valve, with flow monitored downstream.

4. What’s the purpose of the Fuel/Oil Heat Exchanger?

It serves dual roles:

  • Pre-heats fuel (preventing icing).
  • Cools engine oil while warming the fuel.
    There’s also an Air/Oil heat exchanger that activates when fuel flow is low or fuel is already warm.

5. How is engine oil pressurized and circulated?

  • Driven by N2 via the accessory gearbox.
  • Oil flows through a filter, fuel/oil heat exchanger,
  • Lubricates bearings, gearbox, accessory drives.
  • Scavenge pump returns oil to tank; temperature and pressure are monitored.

6. Describe the ignition system and start sequence on the ground.

  • Two ignitors per engine, managed by EEC.
  • Ground start uses one ignitor; in‑flight auto‑start uses both.
  • Starts use DC power chiefly, with standby backup.
  • The APU is primary for start; external power (FWD/AFT) can supplement.

7. When and how is thrust reverse available?

  • Active only on the ground, hydraulically driven.
  • Cascade vanes reverse bypass airflow.
  • Thrust levers must be at idle and moved into interlock.
  • Autothrottle disengages, speed brakes deploy automatically.
  • EICAS warns of ground/air logic faults like ENG REV LIMITED or ENG REV AIR/GND.

8. What are the primary engine indications displayed on EICAS?

Key indications:

  • TPR, N1, EGT are primary.
  • EGT has amber in continuous and red at takeoff/go‑around limits.
  • Red alerts remain until acknowledged; redline exceedances persist.

9. What is the automatic engine start and relight logic?

  • AutoStart uses starter‑generators to drive N2.
  • If APU fails, external power supports start.
  • AutoStart aborts on faults: hung start, hot start, no rotation, etc.
  • In‑flight, auto‑relight tries restart after flameout, detecting low EGT/N1 or stall conditions.

10. Explain the Electronic Engine Control (EEC) modes and transitions.

  • In NORM, engine thrust is based on TPR per thrust lever input.
  • If sensors fail, alternate mode kicks in using N1:
    • Soft alternate: automatic, keeps autothrust active.
    • Hard alternate: manual mode shows commanded/target values.
  • EICAS advises when EEC mode changes using ENG EEC MODE alerts
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