In article , wrote:

On 24 Oct 2004 14:33:05 GMT, (Pechs1) wrote:

Tamas- Otherwise all variable wing planes suck a great deal: heavy,
trouble-prone, cost a lot to maintain, wings mecha takes up precious
place in the fuselage, won't survive battle damage. No wonder the USN is
retiring all Tomcats. BRBR

It wasn't the swept wing that doomed the F-14. In my experience in 2 F-14
squadrons, the wing sweep mechanism was never a maintenance issue.

It's pretty much bulletproof, too, being overbuilt and armored. Wing
sweep problems are really rare. The folks at Pax tested the one wing
stuck aft flyability and landability (I don't remember whether they
tested trappability, though), I think as the result of that actually
happening once. That was fairly recently, like in the last decade, so
it's probably related to system wear.

It is an old design, never modified to it's full capabilities with available
technology. Analog, push rod type flight controls, tube type avionics,
****poor
engines in the majority of the A/C(TF-30).

What really did it in was LRUs, Line-Replaceable Units. These greatly
reduce the amount of plane-side maintenance by moving it to depots.
Instead of repairing or replacing components, the entire defective
unit is pulled out and a new working unit is plugged in. This is
quick and easy.

The LRUs were the result of the military emphasizing ease of
maintenance. With LRUs they increased up time, reduced maintenance
time, and reduced crew size.

We saw a huge improvement in all three at Dryden when we switched from
F-104s to F-18s. The USN saw something similar going from A-7s to
F/A-18s, according to a couple of captains I talked to back in 1990.

I started with Hughes in '78 and LRUs were the design standard then.
Can't speak for the rest of the electronics on the a/c, but the radar & EW
systems were designed as LRUs.

Here's the real difference today:
Prior to the mid-90's all maintenance was 3 levels; flightline, shop level
(local, on-base), and depot. The flightline maintenance comsists of
replacing the black box at the airplane.

The shop level tried to diagnose the problem with the black box, open
it up and replace the faulty assembly inside. This required a LOT of test
and evaluation equipment and highly trained electronics techs.
Sometimes even card repairs were done in the shop.

Anything that could not be diagnosed and fixed in the shop was sent to
the depot for repair.

This 3 level maintenance was the same for both USAF and USN.

Lately, since the mid-90's, contracts have gone to 2 level maintenance.
Getting rid of the intermediate shop has eased a lot of problems;
No expensive test equipment, reduced need for trained techs, less
hardware in the pipeline, less facilities required, etc.
Now, the LRUs are pulled at the flightline and sent directly to the depot
with no attempt to repair at the base.

What allows this to be economical are three things, heavy emphasis
on reliability engineering, improved capability of embedded self-test,
and the FEDEX model of moving hardware fast overnight.

There were LRUs well before the F/A-18, but Mary is right in that the
emphasis on ease of maintenance and reliability paid real
dividends in system availability and uptime, and reduced cost.

--
Harry Andreas
Engineering raconteur