737;power to the buses....

[G-STAW]

Evening everyone,

Ok, ive just started my PPL, im also learning the 737 CBT and FCOM material.

At the moment im studying the APU and electrical systems.....

i understand that the 1 & 2 buses need a power source at all times from one of three sources;

-APU
-External power
-IDG

I work at manchester airport and often witness aircraft coming onto stand unable to turn their engines off persumably as no ex pwr is connected, but why isnt the APU running pre coming on stand?

also when ex pwr is connected, why isnt the APU turned off straight after? the flightdeck has now got an alternative pwr source, is this down to the crew not realising ex pwr is available?

hope a more experienced person cany help,


cheers scott

[Cough]

I work at manchester airport and often witness aircraft coming onto stand unable to turn their engines off persumably as no ex pwr is connected, but why isnt the APU running pre coming on stand?

Prob APU is U/S.

also when ex pwr is connected, why isnt the APU turned off straight after? the flightdeck has now got an alternative pwr source, is this down to the crew not realising ex pwr is available?

Ground power connected does not mean that the aircraft will be air conditioned. Even on a moderate day of 15-20C will lead to much higher temps in the cabin. APU is operated to keep one or maybe two packs working in order to keep the cabin either cool or warm!
Also, during darkness, often APU is kept running until the last pax disembarks as ground power sources can be unreliable, the cabin going almost completely dark when they do fail!

Hope that helps.

[Deaf Tortoise]

In addition to the above, the APU may be off in line with company standard operating procedures:

Pull onto stand, shut down right engine and keep left engine running until ground power connected.

This saves one APU start cycle, supposedly making it need less engineering work, and supposedly resulting in reduced fuel consumption.

Notice that I am not entirely convinced that this is clever or effective.

[CAT1 REVERSION]

You may also notice that more and more of us are pulling on stand with the No'2 eng shutdown. All designed to save fuel in this ever increasing climate.

We have (on the 73 that is) an indication telling us when we have ground power available. Once we have this we transfer the power from either the No'1 gen (if No'2 Eng shutdown) or the apu gen to the GPU, via a simple switch.

We may elect to keep the APU running for cooling, it all depends on the day!

My Airline requests minimal use of APU, mainly to save fuel and cycles - that is why we often do not shut down until GPU available, hope that answers your questions!

[Rainboe]

The Scandinavians have a lot to teach us. The ground crew are ALWAYS waiting when you come onto stand so you have the confidence not to start the APU at all. As soon as the brakes go on, the cable is hooked up within seconds, and you can shut down engines. It saves 50% cycles on APUs which are quite unreliable anyway.

I watched the groundcrew de-icing at ARN a few months ago. Quick, efficient, and the moment the plane pushed, a truck went in ever decreasing circles cleaning up the residue, then went bombing off to the next de-icing. Highly efficient, cheerful, totally helpful, I love operating up there (except for the weather).......they've got to do something wrong sometime! It's the best working environment in the world! They smile too. We need to send the BAA up there and put them right!

[G-STAW]

guys thankyou very much for clearing this up for me, i understand that airlines may have different SOPs, but in the main they all have the same goal.

You may also notice that more and more of us are pulling on stand with the No'2 eng shutdown. All designed to save fuel in this ever increasing climate.

ive deffinatly noticed that on nearly all aircraft pulling onto stand.

G-STAW

[Rainboe]

It's a mystery to me why it is not standard practice to have the groundcrew ALWAYS standing by with ground power as aeroplanes park. It would save APU cycles and fuel. Financially the extra cost is justifiable IF the airport can deliver the goods reliably. It is done elsewhere. But the chaos that passes for airport administration in the UK means that aeroplanes sit there with APUs running and passengers itching to get off whilst the clearance of the stand, delivery of steps, buses and groundstaff resembles a Laurel and Hardy movie. Usually one, often two, and sometimes all 3 are missing! It's a shambles. Airport managers should be sent to Scandinavia to see how to do it. Because they're a joke at the moment.

[G-STAW]

totally agree, i work for servisair at MAN at the moment, and we had an example of this the other day with a thomson 733.

I was working on another stand, and had to wait for a thomson 733 to come on stand and shut its engines down before i could cross behind.(same example per my origional post)

I was waiting about 5 minutes before i lost my patience. I could see the ground crew looking at the cockpit if to say "what the hell are you doing!!", so i pulled alongside a literally screamed "THEY NEED POWER!!", they couldnt thank me enough.......

BTW when meeting and greeting an a/c, connecting power is the second thing we do after chocking. Remember at MAN the power cables are connected to the air bridge, so connectivity time is governed by how quick the dispatcher is....




G-STAW