Jesus nut is a slang term for the main rotor retaining nut or mast nut, which holds the main rotor to the mast of some helicopters. The related slang term Jesus pin refers to the lock pin used to secure the retaining nut. More generally, Jesus nut (or Jesus pin) has been used to refer to any component that is a single point of failure which results in catastrophic consequences.
The term Jesus nut may have been coined by American soldiers in Vietnam; the Vietnam War was the first war to feature large numbers of soldiers riding in helicopters. The term may also have originated with the PBY Catalina, which had two Jesus bolts holding the wing into the fuselage.
If the Jesus nut were to fail in flight, the helicopter would detach from the rotor and the only thing left for the crew to do would be to "pray to Jesus." Real examples of the Jesus nut/pin failing are few and far between. However, the nut/pin must be checked before the flight; in 2000, a mast nut was removed to be repainted and was not restored or checked prior to a test flight. The helicopter crashed within ten minutes of takeoff, killing two. Some more recent helicopter systems do not have a Jesus nut.
Another use for the term is found in rock climbing, in which it refers to the first piece of protection (some of which are also called "nuts") placed on a pitch. This piece must be placed to resist an outward pull as well as a downward pull in order to avoid the possibility of a "zipper", in which the outward pull on the rope from the belayer arresting a falling climber pulls protection pieces from the bottom up. In addition, the Jesus nut prevents the possibility of a factor-two fall onto the belay anchor.
- "Main Rotor Installation diagram". Huey Helicopters UK. Retrieved 28 April 2020.
- Rottman, Gordon L. (2020). Grunt Slang in Vietnam: Words of the War. Open Road Media. ISBN 9781504061704.
Jesus nut The geared rotor retaining nut securing a helicopter blade system to the drive shaft. Aka 'Jesus pin.' One has faith the nut/pin will stay on and not crash, screaming, 'Oh, Jesus!'
- Joiner, Stephen (April 2019). "Legends of an Ocean-Crossing Seaplane". Air & Space. Smithsonian Institution. Retrieved 28 April 2020.
- Levy, Milton; Buckley, Paul; Beatty, John; Brown, Richard; Huie, Robert; Bhansali, Kirt B. (June 1992). Failure Analysis of the Main Rotor Retention Nut from the AH-64 Helicopter, MTL TR 92-39 (PDF) (Report). U.S. Army Materials Technology Laboratory. Retrieved 28 April 2020.
The main rotor retention nut is a flight-critical component that secures the main rotor hub and blade assemblies to the static mast.
- Aviation Investigation Report A00Q0046 (Report). Transportation Safety Board of Canada. 18 December 2001. Retrieved 28 April 2020.
- Aviation Safety Maintainer 1/2002: Fatigue and Complacency - A Potentially Sorrowful Mixture (Report). Transport Canada. 2002. Archived from the original on 2013-05-17.
- Coley, David (2013). High - Advanced Multi Pitch Climbing. Akreative. pp. Section 408 of 5150.
- Long, John; Gaines, Bob (2006). Climbing Anchors (2nd ed.). London: Falcon Press. ISBN 0-7627-2326-2.
- Robert Mason (29 March 2005). Chickenhawk. Penguin Publishing Group. p. 84. ISBN 978-1-101-17515-6.