TF-30 jet engine rebuilds from Vietnam

500-hour overhaul interval for the military TF-30, used to contrast with 30,000-hour commercial engine overhaul intervals, setting up the economic case for blade rejuvenation.

When I worked at the overhaul facility, the overhaul time on a TF-30 turbofan engine was 500 hours. They didn't work for very long before they'd come back for complete rebuilding. That was a military engine — I don't know what the overhaul times are on a military engine right now, I'm not that close to the repair side in the last four years. But on a commercial engine it's 30,000 hours, okay. 30,000 hours, if you were running 24 hours a day — and a land-based turbine generating electricity nearly is — is three or four years.

Tom's 19-year-old summer job at Naval Air Rework Facility, Norfolk. 500-hour engine lifetimes during Vietnam; today 30,000 hours commercial.

They don't oxidize. When I was 19 years old, between my freshman and sophomore years, I got a job working in the Naval Air Rework Facility in Norfolk, Virginia rebuilding engines as an engineering student that summer. The TF30 engines were coming back from Vietnam, and we had to rebuild them and send them back. The engines had 500 hours on them — that was the lifetime of an engine, 500 hours, and you had to rebuild it every 500 hours. Today, 30,000 hours on a commercial engine before you have to rebuild it. So it's not just operating temperature, it's operating lifetime that has improved over this time, in terms of oxidation resistance and other things. From 1972 to 1990 or 1995, you're up to 30,000 hours. We went from better and better alloys to single crystals — single-crystal turbine blades that cost six thousand dollars a blade. You've got a hundred blades on a disc, so six hundred thousand dollars for a replacement set of blades on one disc in one engine. That's why the engines cost five or ten million dollars — it's the blades. Engine companies make maybe twenty percent of their volume on the blades, but forty percent of the profit is on the blades. The vanes are the most valuable part.