Wiktionary
n. (context aviation English) The downward, corkscrew-motion of a disabled aircraft which is unrecoverably headed for a crash.
Wikipedia
In aviation, a graveyard spiral is a dangerous spiral dive entered into accidentally by a pilot who is not trained or not proficient in instrument flight when flying in instrument meteorological conditions (IMC). Other names for this phenomenon include "suicide spiral", "deadly spiral", "death spiral" and "vicious spiral".
Graveyard spirals are most common in nighttime or poor weather conditions where no horizon exists to provide visual correction for misleading inner-ear cues. Graveyard spirals are the result of several sensory illusions in aviation which may occur in actual or simulated IMC, when the pilot experiences spatial disorientation and loses awareness of the aircraft's attitude. In other words, the pilot loses the ability to judge the orientation of his aircraft due to the brain’s misperception of spatial cues.
The graveyard spiral consists of both physiological and physical components. Mechanical failure is often a result but generally not a causal factor, as it is the pilot’s sense of equilibrium which leads to the spiral dive. Flying by "the seat of the pants", and failing to recognize and/or respond to instrument readings is the most common source of controlled flight into terrain where an airplane controlled by a pilot impacts ground.
Usage examples of "graveyard spiral".
He whispered encouragement to her and held the controlwheel with a light and loving touch, trying to ease her nose up out of the graveyard spiral.
They knew the pilot was fighting for control of the crippled machine, fighting the asymmetrical thrust of the remaining engine which was trying to flip the Viscount over into a graveyard spiral, fighting the enormous weight transfer caused by the loss of the port engine.
Its called spatial disorientation followed by the graveyard spiral.