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“Lose One Engine, Lose Half the Power”… and Often More Than Half the Performance

Every multi-engine pilot has heard the line:

“Twins are safer because you have two engines.”


And every experienced multi instructor eventually adds the punchline:

“Lose one engine and you don’t lose half your performance—you can lose most of it.”


That sounds dramatic until you see it in the airplane: same runway, same weight, same day… and suddenly the climb rate that felt effortless becomes a slow struggle—or a steady descent.


Let’s talk about why that happens, what “power loss” really means, what “performance loss” really means, and how to think about it like a pilot instead of like a brochure.



Study this full length lesson (video, podcast, flashcards, and quiz) here: Full Length Lesson >


Power Loss: Yes, You Lose 50% of the Engines (But Not Always 50% of the Thrust)

At a basic level, losing one engine in a twin means you’ve lost roughly 50% of your available shaft horsepower.


But “power available” isn’t the same as “thrust available,” and the airplane doesn’t care about horsepower—it cares about:

  • net thrust

  • net drag

  • and the leftover excess power that becomes climb


And that’s where the performance cliff lives.


Performance Loss: Why It Can Be Massive

Climb is not powered by “total power”—it’s powered by excess power


A key concept:

  • Climb performance = excess power(power available minus power required)


On two engines, many light twins have only a modest amount of excess power. They might cruise fine, but climb isn’t unlimited.


When you lose an engine, power available drops sharply… but power required doesn’t drop nearly as much.


In fact, power required often goes up because of asymmetric drag and control inputs.

So the “excess” can collapse to near zero or negative.


That’s why you can lose one engine and go from:

  • +800 fpm climb to

  • +100 fpm climb or

  • -200 fpm descent


…depending on weight, density altitude, and configuration.


The “More Than Half” Problem: Drag Explodes When an Engine Stops Helping

When one engine fails, you don’t just lose thrust—you gain new sources of drag.


1) Windmilling prop drag

If the failed engine’s prop is windmilling, it becomes a big, ugly drag disk.


Feathering matters because:

  • a feathered prop significantly reduces drag

  • a windmilling prop can destroy single-engine performance


Pilot takeaway: an engine failure is also a propeller drag emergency.


2) Yaw and sideslip drag

With one engine producing thrust, the airplane yaws toward the dead engine. To counter it you use:

  • rudder into the good engine

  • usually a slight bank into the good engine


If you fly with sideslip (not “zero sideslip”), you pay in drag—big time.


Pilot takeaway: good engine-out technique isn’t just “for checkrides.” It’s how you keep the airplane from bleeding away its last bit of climb.


3) Trim and control drag

Rudder deflection is drag. Aileron deflection is drag. If you’re fighting the airplane instead of stabilizing it efficiently, you’re turning thrust into sideways airflow and heat.


4) Configuration drag

Gear down, flaps out, cowl flaps, even a door unlatched—it all matters more when you’re running on thin margins.


Pilot takeaway: you “clean up” quickly in a twin because every knot and every pound of drag matters.


The Critical Moment: Why Losing an Engine After Takeoff Is So Hard

The worst time to lose an engine is when you’re:

  • low

  • slow-ish

  • high power

  • high workload

  • not fully configured (gear, flaps)

  • close to Vmc territory


At that moment, your priorities are:

  1. Maintain control (avoid Vmc loss-of-control trap)

  2. Pitch for the correct speed (safe single-engine speed initially, then Vyse/blue line when stabilized)

  3. Reduce drag (gear up, flaps as required, feather)

  4. Set zero sideslip (don’t waste performance)

  5. Commit to the best plan (continue, land straight ahead, or divert depending on performance and runway/terrain)


The big mistake is trying to “save altitude” with pitch while you’re still unstable. In a twin, pulling for altitude often bleeds airspeed toward Vmc and can lead to a rapid loss of control.


Why “Engine-Out = 80% Performance Loss” Can Be True

Here’s an intuitive way to see the math without doing math:

Imagine the airplane needs a certain amount of power just to maintain level flight at Vyse.

  • With two engines, you have power to maintain level flight plus some extra (excess).

  • With one engine, you might have power to maintain level flight minus the extra drag from asymmetry and windmilling.


So the climb margin—the “extra”—can vanish.


If your two-engine climb rate was driven by a small margin above level-flight power required, losing one engine can erase nearly all of it. That’s why the rate of climb can drop by 80–100% even though “power” only dropped by 50%.


The Factors That Decide Whether You Climb or Descend on One Engine

1) Weight

Heavier = higher power required. Single-engine climb is extremely weight sensitive.


A twin that climbs OEI with two people and half fuel might not climb OEI with four people and bags.


2) Density altitude

High DA hits you twice:

  • less engine power produced

  • worse prop efficiency and aerodynamics


That combination can turn “marginal climb” into “guaranteed descent.”


3) Drag state and technique

  • Feathered vs windmilling prop

  • Gear/flaps configuration

  • Zero sideslip vs sloppy coordination

  • Speed control (Vyse is usually your best shot)


Technique can be the difference between a weak climb and a descent.


4) Engine health and real-world power

The book assumes you’re getting rated power on the operating engine. In reality:

  • mixture might be off

  • engine might not be making full power

  • temps might be limiting

  • turbo behavior (if equipped) changes the game


5) Airframe design

Some twins are built for training convenience; others for hauling; others for speed. The single-engine story varies a lot by type.


“But It’s a Twin—Isn’t It Always Better Than a Single?”

A twin’s real advantage is not “I will climb away on one engine no matter what.”


The advantage is usually:

  • redundancy (electrical, vacuum, alternators, systems) depending on design

  • the possibility of continued flight after an engine failure if conditions allow

  • improved options in cruise when altitude and configuration give you time


But the takeoff/climb phase is still the most unforgiving, and on hot/high/heavy days, the “twin advantage” may be limited to making a controlled landing sooner rather than later.


Practical Pilot Takeaways (The Ones That Keep You Honest)

  • Plan with single-engine performance, not two-engine optimism.

  • Know your single-engine service ceiling and expect it to be low when it’s hot/high/heavy.

  • Treat “feather the prop” as a performance emergency, not a checklist formality.

  • Fly zero sideslip and hold your best single-engine speed.

  • Brief your takeoff plan: when you’ll reject, when you’ll continue, and what you’ll do if performance is negative.


Bottom Line

When a multi-engine airplane loses an engine, the power loss may be around 50%, but the performance loss can be far more because:

  • climb depends on excess power, not total power

  • asymmetric drag and control inputs eat that excess fast

  • windmilling props can be performance killers

  • weight and density altitude can erase OEI climb completely


A twin gives you options—but only if you respect what the airplane can actually do on one engine today, not what it did last winter at sea level.



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