The lifespan of aircraft is generally limited by metal fatigue. This is true for fixed wing aircraft; is it also true for helicopters? What is the determining factor for helicopter useful life?
Helicopters are also subject to metal fatigue and there have been accidents attributed to it but the primary determination is component life times. All of the engine, transmission and rotor parts are lifed and most of the control mechanisms. Depending on the helicopter, there will be many more lifed components.
Some helicopters also have fixed intervals between major overhauls by the manufacturer. For example, the R22 is effectively rebuilt to an "as new" standard by Robinson at 2,200 hours.
Corrosion might also play a part. There may be a time when it is just not economical to continue to repair and service the airframe.
I am a Aerospace Systems Engineer and former Royal Air Force. Although my qualifications and experience are within the avionics arena I feel I can answer this question:
There are basically 3 types of Helicopter and for that fact any aircraft:
- Civil – Private
- Civil – Commercial
The military aircraft have the shorter life in terms of flying hours, the Civil Commercial the longest life in terms of flying hours where as the Civil Private / light aircraft have a very long life in terms of years. A military aircraft can have an airframe file of say 4,000 to 6,000 hours compared to some civil commercial aircraft with an airframe life of 60,000 to even a 100,000 hours.
Now that is for the airframe and ONLY the airframe. The engines, landing gear and most important in terms of helicopters Gear Boxes, Rotor Heads & Blades all have significantly shorter life. One example is that I used to work on the RAF Chinook HC1 i.e aircraft as originally delivered to the RAF by Boeing Vertol. These aircraft where returned to Boeing to be up-graded to the RAF HC2 standard and where returned to the RAF as “New” “Zero Hour” airframes. So, as I say its not always the airframe but the bits that are bolted on to it.
Now, I worked on the RAF HC1 Chinooks from 1988 to 1991. In April 2018 I went to RAF Odiham on a photography shoot event organised by TimelineEvents.Com During that photoshoot I saw aircraft that I had worked on whilst I was on 7 Squadron i.e this particular aircraft must originally been delivered to the RAF in about 1986 making it about 32 years old. However, I would say that the rotor blades will / must be less than 5 years old. Again, another however, the Engines (2 off) and gear box’s (5 off) will of be an indeterminate age but will / must contain a mixture of bits dating from less than 12 months old all the way through to the 32 years age of the original airframe. I think though the most remarkable aircraft was ZA671. It was delivered to the RAF as a HC1 Chinook and returned and rebuilt by Boeing as a HC2.
It crashed whilst in the USA sustain what the RAF calls Cat 4 damage – Cat 5 being a write off and Cat 1 being scratched paintwork. Boeing rebuilt this aircraft as a HC3 Chinook and it’s the one I worked on and is still flying and I have to say that seeing the crash report and photos I am surprised that it was not classed as Cat 5 and I really would not have liked to fly in it during its test flight post accident repair. But the point is that again it depends on what the aircraft is built for, how it's used, how it's maintained, "usefulness”, it's value v. cost of next major servicing.
All of the above will totaled together determine the actual life of an aircraft
Nothing limits the lifespan of a helicopter.
There are many bits and pieces that need to be maintained in order for the helicopter to remain serviceable but so long as there is nothing broken on the helicopter and all overhauled items are within their overhaul limits, and all lifed items are within their life limits... keep on flying.
An Aircrane (Siskorsky S-64) I used to work on just rolled 20,000 hours total time on her fuselage. Still going strong.
I don't know of any machine that has a hard airframe time that puts it out of service permanently. Sorry... no Commercially manufactured helicopter... there may be a kit machine that has a limited life.
I am told that the hourly and calendar service life of many military helicopters are established by the OEM.
Under certain circumstances, that can be extended when scheduled "rework events" are accomplished by the manufacturer or a certified facility.
The military uses industrial rework facilities "depots" to ensure many fuselages remain airworthy beyond established service life.
Fatigue is a problem that limits, if not the life of the helicopter, at least the working life of some of its key elements, in particular of those subject to strong vibration and made from materials (such as aluminum alloys) that have a fatigue limit. Vibration is the main culprit, and it usually comes from the rotors. In rotary-wing aircraft, vibration can be contained, but never fully eliminated.
Most helicopters will go though some sort of "Phase" of "Depot" inspections where different components will be replaced due to life-span requirements. For example; a uh-60L will require a shock strut replacement every 1500 flight hours to prevent a collapse of the strut due to over use.