Question for all experts out there!
I've just been to PRG this weekend and noticed that all Aircraft had their APU's running while parked at the gate.
However, it looked to me that PRG is equipped with External Power supplies - isn't that what those large yellow hose is for?
Why do they use the APU rather than External Power?
Thanks for any info!
Pilatusguy
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- L410Turbolet
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RE: APU Usage At PRG
Good question, didn't notice that myself but I will be flying to PRG tommorow so I will try to remember and ask.
RE: APU Usage At PRG
Hi
I have never been to PRG, only worked as a ramp rat at KPIT. The large yellow hose you described sounds like the ground HVAC system (heating and cooling). This is normally stored under the jet bridge or on a portable and plugs in at one or more various points on the aircraft. The ground power cables are usually black and have a 6 pin connector. This attaches to the aircraft normally on the F/O side of plane almost right in line with the nose gear. Coincidently its the same panel that the pushback driver plugs into.
My guess as to the APU running, if its a short turn around flight, its easier to run the APU then to wait and have the APU start up, then remove GPU (ground power). Also most airlines start the APU (correct me if I'm wrong on this guys) in flight prior to landing. So since its still running and the turn time would be short, thats one less cycle (startup/shutdown) that the APU would have to endure.
Another thing, with the APU running, you can also run the A/C packs on the aircraft and cool or keep cool the aircraft better since the airflow from the APU has much more force. The ground unit cooling or heating doesn't have the airflow to cool on a really hot day or heat for that matter in the winter.
Hope that helps you!!
Baw2198
I have never been to PRG, only worked as a ramp rat at KPIT. The large yellow hose you described sounds like the ground HVAC system (heating and cooling). This is normally stored under the jet bridge or on a portable and plugs in at one or more various points on the aircraft. The ground power cables are usually black and have a 6 pin connector. This attaches to the aircraft normally on the F/O side of plane almost right in line with the nose gear. Coincidently its the same panel that the pushback driver plugs into.
My guess as to the APU running, if its a short turn around flight, its easier to run the APU then to wait and have the APU start up, then remove GPU (ground power). Also most airlines start the APU (correct me if I'm wrong on this guys) in flight prior to landing. So since its still running and the turn time would be short, thats one less cycle (startup/shutdown) that the APU would have to endure.
Another thing, with the APU running, you can also run the A/C packs on the aircraft and cool or keep cool the aircraft better since the airflow from the APU has much more force. The ground unit cooling or heating doesn't have the airflow to cool on a really hot day or heat for that matter in the winter.
Hope that helps you!!
Baw2198
"And remember, Keep your stick on the ice"--->Red Green
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- pilatusguy
- Posts: 302
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RE: APU Usage At PRG
Thanks Baw2198. Guess it was the HVAC that I meant. However, APU was running - maybe L410Turbolet can ask in PRG tomorrow
Cheers
Cheers
RE: APU Usage At PRG
I'm not familiar with the gate power setup at PRG. Usually you have inverters at each gate that convert 480V 50Hz or 60 HZ into 115V 400Hz for AC. If there is a power failure in the 400Hz inverter feeder circuit you can have gate power at all gates fail. Normally each gate has it's own inverter, so if it is an inverter problem it is usually limited to one gate.
757 Most beautiful airliner in the sky!
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- L410Turbolet
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RE: APU Usage At PRG
I was told by one of the ground crew guys at PRG airport that the reasons are:
a) it's not worth it to shut down APU during a quick turnaround
b) questionable reliabilty of the GPU
My question: Are power failures of GPU's common, or is it PRG's specialty?
a) it's not worth it to shut down APU during a quick turnaround
b) questionable reliabilty of the GPU
My question: Are power failures of GPU's common, or is it PRG's specialty?
RE: APU Usage At PRG
L410Turbolet
GPU power failures are really a function of one or more of three things.
1. The age of the GPU.
No explanation necessary.
2. The MX program for the GPU.
No explanation necessary.
3. The suitability of the GPU for the application.
GPUs are rated in KVA - kilovolt-amps. Many of today's AC electrical systems draw far more amperage than that of older generations of AC. If the GPUs KVA rating is not upgraded to meet this demand they will not be able to power newer AC without failure. They might work OK when only the lights and instruments are powered but fail when an electric-hydraulic pump is started.
As for PRG's GPU problems, I'm not familiar with the specifics. But I'd venture to guess they could be attributed to one or more of the above mentioned situations.
Dl757md
GPU power failures are really a function of one or more of three things.
1. The age of the GPU.
No explanation necessary.
2. The MX program for the GPU.
No explanation necessary.
3. The suitability of the GPU for the application.
GPUs are rated in KVA - kilovolt-amps. Many of today's AC electrical systems draw far more amperage than that of older generations of AC. If the GPUs KVA rating is not upgraded to meet this demand they will not be able to power newer AC without failure. They might work OK when only the lights and instruments are powered but fail when an electric-hydraulic pump is started.
As for PRG's GPU problems, I'm not familiar with the specifics. But I'd venture to guess they could be attributed to one or more of the above mentioned situations.
Dl757md
757 Most beautiful airliner in the sky!
RE: APU Usage At PRG
Hi, many airlines advise their pilots to keep the APU running because of the extremely high costs some airports charge the airline for use of GPU and heaters(cooling equipm.).
You read this advise often in Lufthansa flightplan etc. handouts.
You read this advise often in Lufthansa flightplan etc. handouts.
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- sabenapilot
- Posts: 3516
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RE: APU Usage At PRG
The specific problem with Prague is that the groundcrew do not want to approach the plane unless all its engines are shut down.
This means the plane must have it's APU running before shutting down, or else it would sit without electricity on the ramp, something not really advisable to do with pax still on board (emergency lights on and so)
Since the APU has been started and the biggest cost of the use of APU is the start cycle (and not so much the fuel consumed) most pilots tend to keep the APU running for the short period of time spent on the ground prior to start and push (where they will again need their APU)
If the groundcrew in Prague would only have the flexibility to plug in the APU the moment the plane reaches the gate, many airplanes would not have to start their APU and would stay on GPU till shortly before starting up. It would save cost for the airlines and would make the apron of Prague a much quieter place....
This means the plane must have it's APU running before shutting down, or else it would sit without electricity on the ramp, something not really advisable to do with pax still on board (emergency lights on and so)
Since the APU has been started and the biggest cost of the use of APU is the start cycle (and not so much the fuel consumed) most pilots tend to keep the APU running for the short period of time spent on the ground prior to start and push (where they will again need their APU)
If the groundcrew in Prague would only have the flexibility to plug in the APU the moment the plane reaches the gate, many airplanes would not have to start their APU and would stay on GPU till shortly before starting up. It would save cost for the airlines and would make the apron of Prague a much quieter place....
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