A while ago I met a corporate CJ4 pilot for avionics testing. I asked about a GPU and he told me that he did the math and running one of the engines is cheaper than the usual GPU charge of European airports.
Particularly as running an engine on the ground doesn’t count toward engine programs, engine cycles or TBO.
Would be interesting to know the actual amp draw for: starting, aircon, avionics or any combination of those.
Is this a standalone or mains-powered GPU?
You would not get far running aircon from batteries.
How long before start can you get your engine running? Does the same “noise ban” apply as it does for the APU?
JasonC wrote:
Particularly as running an engine on the ground doesn’t count toward engine programs, engine cycles or TBO.
Theoretically, it does. Our (non-FADEC) engines don’t have a counter, so it’s not recorded. However, I already had my first turbine failure and know that these things suffer from usage, therefore I keep the number of starting cycles as low as possible. If you would count the engine starts on the ground as cycles, then every engine start costs as much as an hour of flight which is certainly more expensive than even the most expensive GPU.
Michael wrote:
Would be interesting to know the actual amp draw for: starting, aircon, avionics or any combination of those.
I only know the (rough) figures for out 550 and 560 Citations: Starting – In the region of 500A; Aircon – around 100A; Avionics – 50A (but we have CRT displays that draw a lot more current than LCD ones). So running the avionics and aircondition on the ground plus cabin fans will require in the region of 200A steady supply.
In our operation, we have mains powered GPUs in the hangar for maintenace and database updates and suchlikes. Other than that, we never use a GPU. Outside the simulator, I have not yet done a ground power engine start on a Citation in over 2000hr on type…
Before that, I was flying a Metroliner which really required a GPU for getting the engines running (battery starts were really only used when absolutely no GPU could be organised). They charged us anything between 0 and 200 Euros for the GPU aroung Europe. With the average somewhere near 50 Euros I reckon.
what_next wrote:
Theoretically, it does. Our (non-FADEC) engines don’t have a counter, so it’s not recorded. However, I already had my first turbine failure and know that these things suffer from usage, therefore I keep the number of starting cycles as low as possible. If you would count the engine starts on the ground as cycles, then every engine start costs as much as an hour of flight which is certainly more expensive than even the most expensive GPU.
For the Pratt 615, an engine cycle is defined as startup, takeoff, shutdown. I am not suggesting running an engine on the ground involves no wear, of course it does, but I am referring to the charging basis for the programs.
Out of interest, was there ever any more follow up on your engine failure as to why it happened?
In our operation, we have mains powered GPUs in the hangar for maintenace and database updates and suchlikes. Other than that, we never use a GPU. Outside the simulator, I have not yet done a ground power engine start on a Citation in over 2000hr on type…
I expect that is what I am going to have to do.
JasonC wrote:
Out of interest, was there ever any more follow up on your engine failure as to why it happened?
It was caused by a “casting anomaly” of a turbine blade according to the report provided by the manufacturer. A rare manufacturing defect that was not caught during the x-ray and ultrasonic testing of the blades before installation. The engine was outside warranty (5 years or 2500hr) but the manufacturer did what he could to keep his cutomer (my employer) happy. The final bill for the repair was still impressive… but some of the repairs count towards the next overhaul which will lower the cost for that.
