Definition
The maximum density altitude a multiengine airplane can maintain in level flight with one engine inoperative, the operating engine(s) at maximum continuous power, the inoperative propeller feathered, landing gear and flaps retracted, and the airplane banked into the operating engine at the optimum bank angle.
Plain English
The highest altitude a twin-engine airplane can hold steady when one engine has quit and the other is doing all the work. Above this altitude, the airplane cannot stay level on one engine and will slowly descend.
Context Anchor
Encountered in multiengine performance planning and in engine-failure discussions, especially when deciding whether an airplane can climb, hold altitude, or must descend after losing an engine.
Derivation
Ceiling here uses the building sense -- the upper limit you cannot go past. The term simply states the ceiling that applies when you are reduced to a single engine.
Why Pilots Care
Determines whether a multi-engine aircraft can safely cross high terrain if one engine fails.
Grounding Statement
After one engine fails, the airplane may reach an altitude condition where the remaining engine can only slow the descent or barely hold altitude, not climb away.
Intuition Check
Do not read single-engine ceiling as a height marked on the altimeter only. It is a performance limit based on conditions, airplane weight, and one-engine capability.
Example Sentence 1
Their planned cruise altitude of 12,000 feet was well above the airplane's single-engine ceiling, so the pilot briefed a drift-down plan in case of engine failure.
Example Sentence 2
With a single-engine ceiling of 7,500 feet, the flight plan kept the route over terrain no higher than 6,000 feet.