ME.1
Why the Second Engine Changes Everything
Understand what the second engine actually buys you, why an engine failure in a light twin is a performance and control problem at the same time, and why the accident record for light twins turns on the pilot rather than the airplane.
References: FAA-H-8083-3 (AFH ch. 13); POH/AFM
Quick Review
Conversational Q&A — quiz yourself before the oral.
Redundancy and performance — but only conditionally. The AFH is blunt about it: the performance and system redundancy of a multiengine airplane only increase safety if the pilot is trained and proficient (AFH ch. 13).
The airplane doesn't save you. Training and proficiency do. That is the entire premise of the class rating.
Because climb comes from excess power, not total power.
- Loss of one engine is a loss of 50 percent of power
- That reduces climb performance by 80 to 90 percent (AFH ch. 13)
Level flight consumes most of what the engines produce. What's left over is climb — and one engine's worth of thrust barely covers the level-flight requirement.
Performance and control.
- Performance — climb capability may be marginal or simply nonexistent
- Control — asymmetrical thrust yaws and rolls the airplane toward the dead engine
A single-engine airplane only hands you a performance problem. A twin hands you both at once, and the AFH says attention to both is crucial to safe OEI flight (AFH ch. 13).
- Small multiengine airplane — a reciprocating or turbopropeller-powered airplane with a maximum certificated takeoff weight of 12,500 lb or less
- Light twin — not formally defined in the regulations; the AFH uses it for a small multiengine airplane of 6,000 lb or less maximum certificated takeoff weight (AFH ch. 13)
Generally, no — and this is the single most important thing to understand about the airplane you're about to fly.
Under the historical part 23 requirements, for an airplane of 6,000 lb or less maximum weight with VSO of 61 knots or less, the single-engine rate of climb at 5,000 ft MSL must simply be determined. The rate of climb could be a negative number. There is no requirement for a positive single-engine rate of climb at 5,000 feet or any other altitude (AFH ch. 13).
- Red radial line — VMC, the minimum control speed. This is the control problem.
- Blue radial line — VYSE, best rate of climb with one engine inoperative. This is the performance problem.
The AFH's chapter summary frames the whole discipline around exactly these two markings (AFH ch. 13). Your own numbers come from your AFM/POH — never assume a number you learned in another twin.
- Loss of directional control
- Loss of performance
- Loss of flying speed
All three have equal potential to be lethal. Loss of flying speed is not a factor, however, when the airplane is operated with due regard for directional control and performance (AFH ch. 13).
Analysis of engine failures on takeoff reveals:
- A very high success rate of off-airport engine-inoperative landings when the airplane is landed under control
- A very high fatality rate in stall-spin accidents when the pilot attempts flight beyond the performance capability of the airplane (AFH ch. 13)
The airplane is rarely the variable. The decision is.
Attempting to fly when it is not within the performance capability of the airplane to do so. The AFH's verdict: an accident is inevitable.
Remaining airborne and bleeding off airspeed in a futile attempt to maintain altitude is almost invariably fatal. Landing under control is paramount (AFH ch. 13).
No multiengine airplane is approved for spins, and their spin recovery characteristics are generally very poor. Very few twins have ever been spin-tested — none are required to be (AFH ch. 13).
Practice spin avoidance and stay alert to the setups that produce one: VMC demonstrations, stall practice, slow flight, or any condition of high asymmetrical thrust at low speed and high AOA.
The airplane manufacturer. The AFM/POH guidance and procedures take precedence over any general recommendation in the AFH or in any training text — including this one (AFH ch. 13).
Every speed in this guide is a concept. Every number is in your book.
Because the OEI flight regime has no analog in single-engine flying. Mastery of OEI flight is only one aspect of safe multiengine flying, but it is the aspect that distinguishes the class — and the modern, well-equipped multiengine airplane can be remarkably capable when the pilot is proficient (AFH ch. 13).
Deep Dive
Where the climb performance goes
The examiner will want you to explain the 80-to-90-percent figure rather than recite it. The AFH gives a hypothetical you can walk through out loud.
- Rate of climb — altitude gained per unit of time (fpm)
- Climb gradient — altitude gained per 100 feet of horizontal travel, expressed as a percentage. A gain of 1.5 ft per 100 ft (15 ft per 1,000, 150 ft per 10,000) is a 1.5 percent gradient (AFH ch. 13)
Gradient matters because, unlike rate of climb, climb gradient is affected by wind — improved by a headwind component, reduced by a tailwind (AFH ch. 13). Obstacles care about gradient, not rate.
Certification basis — why "what year is it" is the wrong question
The examiner may probe whether you understand that your airplane's performance guarantees come from the rules in effect at type certification.
No. The performance characteristics of an airplane depend upon the rules in effect during type certification and do not depend on the production year after certification (AFH ch. 13).
Don't confuse the date of type certification with the airplane's model year — the type certification basis of many multiengine airplanes dates back to the Civil Aviation Regulations (CAR) 3 (AFH ch. 13).
The current amendment to 14 CFR part 23 (81 FR 96689) went into effect December 30, 2016, covering normal category airplanes with 19 or fewer passenger seats and 19,000 lb or less maximum certificated takeoff weight (23.2005(a)).
Airplanes are sorted into certification levels 1 through 4 by passenger seating (23.2005(b)) and into two performance levels by speed (23.2005(c)).
Example: a level 2 low-speed airplane that does not meet single-engine crashworthiness requirements needs a climb gradient of at least 1.5 percent at 5,000 ft pressure altitude in the cruise configuration (23.2120(b)(1)).
Two categories (AFH ch. 13):
More than 6,000 lb and/or VSO more than 61 knots — single-engine rate of climb at 5,000 ft MSL must be at least 0.027 × VSO² fpm. For airplanes type certificated February 4, 1991 or later, expressed instead as a 1.5 percent climb gradient. (The gradient is not a direct equivalent of the 0.027 VSO² formula.)
6,000 lb or less and VSO 61 knots or less — the rate of climb must simply be determined, and may be negative. For light twins type certificated February 4, 1991 or later, the gradient (positive or negative) is simply determined.
The honest framing
Very. The AFH notes that the modern well-maintained reciprocating engine is remarkably reliable (AFH ch. 13).
That's worth holding alongside everything else in this guide. Training risk is real: stall-spin accidents in training for emergencies rival the number of stall-spin accidents from actual emergencies (AFH ch. 13). The discipline you're learning is meant to make both columns smaller.