Hacker News Reader

Comment by notahacker | Hacker News Reader

The difference with helicopters is that unlike the MiG-21, there's significant commercial demand for their use (it just happens to be in a bit of a trough at the moment) and most of the costs are proportionate to how many flying hours it gets - they don't have the sharp year on year depreciation associated with commercial fixed wing aircraft because innovation is slower, design lives are longer and required maintenance intervals generally aren't measured in years. Historically, helicopters have even been known to appreciate in value over several year economic cycles.

If I wanted to make money, I'd much rather have one AW109A than 4 Mig 21s.

View on HN

> Required maintenance intervals generally aren't measured in years

Isn't that a bit misleading? There are components and systems that only need servicing every few years, but general practice with helicopters is phased inspections every m months (the military generally does every 6 months).

Sure, helicopters are easier to work on and generally require less maintenance per flight hour than jets do, but they're still aircraft, so they're greedy and needy.

My experience in the military was that phased inspections on fighter aircraft was done every N flight hours, not based on a fixed amount of time, I would assume helicopters are the same, but I was under the impression that helicopters required more maintenance, not less, due to the increased mechanical complexity, but I never got to work on those, so I really have no idea.

Huh. When I was an engineer (civilian) working on helicopters at a test squadron (HX-21), they put their aircraft in phase every 180 days, flight hours or no. But I guess the key words are "test squadron".

The rotor hub, transmission, and tail rotor are mechanically complex, but there are fighter aircraft out there with way more mechanically complex systems (F-35B lift system comes to mind).

It could be that it has a special, experimental, or provisional airworthiness certificate, in which case that certification determines inspections rather than FARs. If it had none of those, and wasn't an aircraft used for hire, then the annual inspection applies. And all that means is that the requirements for an annual inspection are met within the previous 12 calendar months, so they could certainly do 1/2 the required annual inspection every 180 days.

You may be right. I am not at all knowledgeable about airworthness certificates. I did assist with supplying engineering documentation for flight clearances, but those are not the same thing.

The military pretty much follows FARs, and where they don't, they're more strict. I'd expect the military does either 100 hour or progressive inspections, hour defined as "time in service" which for most aircraft is flight time as measured by a landing gear squat switch. Many general aviation aircraft will use tachometer time where they don't have such an flight time meter. Progressive inspections pretty much are 100 hour inspections but get broken down to e.g. 4 inspections every 25 hours, and the 100 hour inspection is only considered complete once the last inspection for that cycle is done. But they could do 10 inspections every 10 hours, or whatever.

I'm thinking less of the periodic inspections which aren't that expensive in the scheme of aircraft ownership costs, and more of the fact your average commercial jet needs heavy checks which essentially rebuild the aircraft every six years at a multimillion dollar cost even if it hasn't been heavily used. afaik the mandatory time-scheduled heavy maintenance on most helicopter types is comparatively limited and it's replacing components - according to flying hours rather than age - that costs virtually all the money.

Reply on news.ycombinator.com