What makes an aircraft qualify as a 'complex aircraft' according to the FAA?

Under 14 CFR 61.1, a complex aircraft is defined as one that has all three of the following features: retractable landing gear, wing flaps, and a controllable-pitch propeller. An aircraft must have all three characteristics simultaneously to meet the definition — lacking even one disqualifies it from being classified as complex. This definition is important because specific training and endorsement requirements apply before a pilot may act as pilot in command of such an aircraft.

Do you need a special endorsement to fly a complex aircraft?

Yes. Under 14 CFR 61.31(e), a pilot must receive ground and flight training in a complex airplane from an authorized instructor and obtain a one-time logbook endorsement before acting as pilot in command of a complex aircraft. This requirement applies regardless of certificate level, so even a certificated private pilot must hold the endorsement before flying complex aircraft as PIC. The endorsement certifies that the pilot has demonstrated proficiency in the systems and procedures unique to complex airplanes.

Why do commercial pilot applicants specifically need complex aircraft training?

The FAA requires commercial pilot applicants to log at least 10 hours of training in a complex airplane, turbine-powered airplane, or FAA-approved aviation training device representing such aircraft, as stated in 14 CFR 61.129. This requirement exists because commercial operations often involve higher-performance aircraft with more sophisticated systems, and pilots must demonstrate they can manage retractable gear, variable-pitch propellers, and flaps proficiently and safely. Proper training in these systems is emphasized in the Airplane Flying Handbook (FAA-H-8083-3) to ensure commercial pilot candidates develop sound aeronautical decision-making habits with complex equipment.

Complex Aircraft Definition and Endorsement Requirements

What Makes an Aircraft "Complex"?

The Federal Aviation Regulations draw a precise line around the term complex aircraft. Under 14 CFR 61.1(b), a complex airplane is one that has all three of the following features:

Retractable landing gear — the gear retracts into the fuselage or wings during flight rather than remaining fixed in the airstream.
Wing flaps — movable surfaces on the trailing edge (or leading edge) of the wing that increase lift and drag on demand.
A controllable-pitch propeller — a propeller whose blade angle can be changed in flight, either manually or automatically through a constant-speed governor.

All three features must be present simultaneously. An airplane with retractable gear and flaps but a fixed-pitch propeller is not complex. An aircraft with a constant-speed prop and flaps but fixed gear is also not complex. This "all three" rule is one of the most commonly tested points on the FAA knowledge exam.

There is one important exception carved out by the regulation: a multiengine airplane that is equipped with reciprocating engines and has a sea-level critical altitude (meaning its engine performance does not drop off with altitude in the normal way) may qualify as complex even if it lacks one of the three features — but this is a narrow technical carve-out that rarely affects practical training decisions. Focus your study energy on the standard three-feature definition.

Why These Three Systems Matter Operationally

Each system in the complex definition adds workload, capability, and risk. Understanding why they matter helps you remember the definition and manage these airplanes safely.

Retractable Landing Gear

Retractable gear dramatically reduces aerodynamic drag, improving cruise speed and fuel efficiency. The trade-off is a new failure mode: landing with the gear up. Gear-up landings are among the most embarrassing — and expensive — accidents in general aviation. Complex training specifically prepares pilots to build reliable gear-check habits, use checklists religiously, and respond to warning horn activation or gear-position indicator anomalies. The GUMPS check (Gas, Undercarriage, Mixture, Propeller, Switches/Seatbelts) is a widely used pre-landing mnemonic in complex aircraft to ensure the gear is down and locked before touchdown.

Wing Flaps

Flaps allow slower approach speeds, steeper descent angles, and shorter landing rolls. While flaps appear on many simple aircraft, they are included in the complex definition because complex aircraft typically have more sophisticated, electrically or hydraulically actuated flap systems. Improper flap use — such as retracting flaps abruptly at low airspeed — can cause a rapid loss of lift that the pilot may not have the altitude to recover from. Training in a complex aircraft therefore reinforces disciplined, phased flap management.

Controllable-Pitch Propeller

A constant-speed propeller keeps engine RPM nearly constant by automatically varying blade pitch. The pilot manages power with both the throttle (controlling manifold pressure) and the propeller control (controlling RPM). This coordination is unfamiliar to pilots who have only flown fixed-pitch aircraft. Incorrect power management — such as increasing RPM before increasing manifold pressure on a turbocharged engine, or reducing manifold pressure after reducing RPM during the descent — can cause overboosting or excessive engine wear. Complex training instills the correct sequencing: generally, when adding power, increase RPM first and then manifold pressure; when reducing power, reduce manifold pressure first and then RPM.

The Endorsement Requirement: 14 CFR 61.31(e)

The endorsement requirement for complex aircraft is found in 14 CFR 61.31(e). No person may act as pilot-in-command (PIC) of a complex airplane unless that person has:

Received and logged ground and flight training from an authorized instructor in a complex airplane, or in a full flight simulator or flight training device (FTD) that is representative of a complex airplane; and
Been found proficient in the operation and systems of a complex airplane; and
Received a one-time logbook endorsement from an authorized instructor certifying proficiency.

The endorsement is a one-time requirement — once you receive it, it does not expire and does not need to be renewed. However, it is your legal authorization to act as PIC of any complex airplane going forward. Lose your logbook, and proving you hold the endorsement becomes very difficult, so keep a digital backup or certified copy.

Note carefully that the regulation says "act as pilot-in-command." A student or other pilot may fly a complex airplane from the right seat under the supervision of a CFI who is acting as PIC without holding the endorsement — but the moment you are the PIC, the endorsement is required.

How the Complex Requirement Fits Into Commercial Pilot Training

The complex endorsement is particularly important at the commercial pilot level because 14 CFR 61.129 requires that a commercial pilot applicant log a specified number of hours in a complex airplane (or a turbine-powered aircraft) as part of the practical test prerequisites. Specifically, for an airplane single-engine commercial certificate, the applicant must log at least 10 hours of flight training in a complex airplane (or turbine-powered airplane, or technically advanced airplane [TAA] as defined in the regulation). This training must include the maneuvers and procedures required by the commercial ACS.

For the airplane multiengine commercial certificate, the 10-hour complex/turbine/TAA requirement may be met with a multiengine airplane that is itself complex — which many twins are, since they typically have retractable gear, flaps, and constant-speed props.

Practically, this means most commercial students train in aircraft such as the Cessna 172RG, Piper Arrow, Beechcraft Bonanza, or similar retractable-gear singles, all of which meet the complex definition. Before logging a single hour of PIC time in one of these airplanes, the endorsement under 61.31(e) must already be in the logbook.

Complex vs. High-Performance: Don't Confuse Them

Students frequently mix up the complex and high-performance endorsement requirements. They are separate and distinct:

A high-performance airplane is defined under 14 CFR 61.31(f) as one with an engine of more than 200 horsepower. The endorsement requirement is the same structure — ground training, flight training, logbook endorsement — but the trigger is engine power, not aircraft features.
An airplane can be complex but not high-performance (e.g., a Piper Arrow with a 180 hp engine).
An airplane can be high-performance but not complex (e.g., a high-horsepower fixed-gear tailwheel aircraft).
An airplane can be both complex and high-performance (e.g., a Beechcraft Bonanza A36 with a 300 hp engine), in which case the pilot must hold both endorsements.

On the knowledge test, a question may describe an airplane and ask which endorsements are required. Parse the description carefully: count horsepower for the high-performance question, and check for all three features for the complex question.

Memory Aid

To remember the three features that define a complex airplane, use the phrase "Real Flyers Control" — Retractable gear, Flaps, Controllable-pitch propeller. All three must be present. If any letter is missing from the cockpit, it's not a complex airplane.

Common Test Traps

"Two out of three" is not enough. An airplane must have retractable gear, flaps, AND a controllable-pitch prop to be complex. Missing even one disqualifies it.
The endorsement never expires. Unlike a flight review, the 61.31(e) complex endorsement is a permanent one-time entry. Do not confuse it with currency requirements.
Complex ≠ High-Performance. Engine horsepower (more than 200 hp) determines high-performance; the three-feature set determines complex. A 180 hp Piper Arrow is complex but not high-performance.
Logging PIC time triggers the endorsement requirement. Flying as a safety pilot or student under a CFI's PIC authority does not require the endorsement, but acting as PIC does — even for a solo flight around the pattern.
Simulators can count. Ground and flight training in an approved full flight simulator or FTD that is representative of a complex airplane can satisfy the 61.31(e) training requirement, even if actual complex airplane flight time is limited.