Autothrottle

Understanding Autothrottle in Modern Aircraft

The autothrottle (A/T) is an aircraft system that automatically controls engine thrust to achieve a pilot- or system-selected target, typically a constant engine power setting (N1 or EPR) or a commanded airspeed (IAS/Mach). By managing thrust precisely, it reduces pilot workload, supports stabilized approach criteria, and improves performance and fuel efficiency across all phases of flight. In ATPL training and airline operations, correct A/T use is closely tied to procedures and aviation regulations governing takeoff thrust setting, climb profiles, and approach minima.

Autothrottle operating modes are broadly grouped into speed-hold and thrust-hold functions. In SPEED mode, the A/T continuously adjusts thrust to maintain the selected IAS or Mach, which is especially useful during climbs, descents, and approaches. In thrust-hold modes (often labeled N1 or EPR), the system commands a fixed thrust setting—such as takeoff, climb, or cruise thrust—while pitch controls speed. For takeoff, the A/T can be used to set and hold the required takeoff thrust (e.g., N1), ensuring the target is achieved on the ground run. As the aircraft climbs, a modern thrust computer/FADEC automatically refines target N1 to account for changing temperature and pressure, keeping the commanded thrust within the selected limit (TO/GA, CLB, CRZ). These functions are standardized in airline procedures and taught in ATPL systems modules.

Understanding A/T interaction with autopilot modes is essential. With the autopilot in ALT HOLD, pitch is used to maintain altitude, so the A/T typically operates in SPEED mode to hold the selected IAS. In a climb with the autopilot in V/S (vertical speed) mode, the A/T again manages IAS in SPEED mode while pitch meets the selected rate. During both automatic and manual ILS final approaches, the A/T can be used in SPEED mode to stabilize approach speed, supporting consistent energy management and compliance with stabilized approach criteria. Mode awareness is critical: crews confirm A/T engagement and active modes on the Primary Flight Display (PFD) flight mode annunciator (FMA), make standard callouts, and monitor that commanded speed or thrust agrees with the briefed procedure and aircraft performance.

What the Autothrottle Question Bank Covers

• Purpose of A/T: maintaining constant engine power or airspeed for workload reduction and stability.
• Use on takeoff: arming/engaging A/T, setting and holding takeoff thrust (e.g., N1) on the ground run.
• Key modes: SPEED (IAS/Mach hold) versus thrust-hold (N1/EPR) and their application in different phases.
• Autopilot coupling: ALT HOLD and V/S interactions with A/T in SPEED mode to control IAS.
• ILS operations: employing A/T in SPEED mode on both manual and automatic approaches for stabilized flight.
• Thrust management/FADEC: automatic N1 adjustment with altitude and temperature during climb.
• Mode awareness: verifying A/T status and active modes on the PFD/FMA and following SOP callouts.
• ATPL relevance: systems knowledge, procedures, and best practices aligned with aviation regulations.