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RL CRJ Question (Last One - I Promise) - Noise Prior to Pushback


jay jay

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As noted on my previous post, just flew a couple of legs in an AA CRJ.    One other thing I noted - just before pushback, I heard a loud mechanical noise (sounded like an electrical or hydraulic motor from under the floor in the vicinity of the LG bay area).  Ran for about 20-30 seconds.   Any idea what this was?   Heard it on both flights.

 

 

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22 hours ago, jay jay said:

As noted on my previous post, just flew a couple of legs in an AA CRJ.    One other thing I noted - just before pushback, I heard a loud mechanical noise (sounded like an electrical or hydraulic motor from under the floor in the vicinity of the LG bay area).  Ran for about 20-30 seconds.   Any idea what this was?   Heard it on both flights.

 

 

You must be getting some immersion factor I have either not noticed or don't have.  I will pay attention to this and see if it is audible on my end.  Could it be a MSFS sound for the push back tug lifting the nose wheel?

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On 3/20/2022 at 11:39 AM, jay jay said:

As noted on my previous post, just flew a couple of legs in an AA CRJ.    One other thing I noted - just before pushback, I heard a loud mechanical noise (sounded like an electrical or hydraulic motor from under the floor in the vicinity of the LG bay area).  Ran for about 20-30 seconds.   Any idea what this was?   Heard it on both flights.

 

 

The number 3 hydraulic pump is above the landing gear bay. It is started before brake release on pushback and runs continuously until the aircraft is parked at the gate after landing.

 

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4 hours ago, JRBarrett said:

The number 3 hydraulic pump is above the landing gear bay. It is started before brake release on pushback and runs continuously until the aircraft is parked at the gate after landing.

 

That's a loud pump (although the A320 has something even louder that activates around the same time)!   Any idea if it's 3A or 3B?   The checklist that Aerosoft provides has 3A turned on early during the cockpit preparation phase (any idea why they would need a hydraulic at that stage of the starting process?).   The remaining three pumps (1, 2 and 3B) are listed as starting during the originating check which is still somewhat early in the startup process.   That being said, all 4 pumps are also shown as being activated (either auto or for 3A, on) during the pushback checklist as well so I guess I'm not clear when the pumps are actually supposed to be turned on, as they are referenced in three separate checklist phases. 

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2 hours ago, jay jay said:

That being said, all 4 pumps are also shown as being activated (either auto or for 3A, on) during the pushback checklist as well so I guess I'm not clear when the pumps are actually supposed to be turned on, as they are referenced in three separate checklist phases. 

3A is electric and active as soon as you flip the switch.  1 and 2 are engine-driven during normal ops, so in Auto they won't kick on until the engines are started.

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10 hours ago, jay jay said:

That's a loud pump (although the A320 has something even louder that activates around the same time)!   Any idea if it's 3A or 3B?   The checklist that Aerosoft provides has 3A turned on early during the cockpit preparation phase (any idea why they would need a hydraulic at that stage of the starting process?).   The remaining three pumps (1, 2 and 3B) are listed as starting during the originating check which is still somewhat early in the startup process.   That being said, all 4 pumps are also shown as being activated (either auto or for 3A, on) during the pushback checklist as well so I guess I'm not clear when the pumps are actually supposed to be turned on, as they are referenced in three separate checklist phases. 

 

It definitely is a loud pump. In the cockpit preparation phase you would check the hydraulic fluid quantity and temperatures to see if they are within limits. You also need normal hydraulic pressure for the stall test and to check brake wear indicator pins during the walkaround.

 

After that, usually 1, 2 and 3B go in Auto mode. You could leave the 3A pump on if you wish, it is designed to run continuously in flight and can do so on the ground as well as long as temperatures stay within limits. The other systems have a heat exchanger with fans to cool the fluid in addition to running through the fuel tanks and being cooled by the fuel as well. System 3 does not have a heat exchanger and solely relies on cooling by fuel. So on hot days the better option may be to keep the pump off as much as possible. It is then needed to switch it On once you do the cleared to start check before pushback. 

 

Pumps are obviously also wear items, so the less they run, the less they wear. When I fly, 3A goes off after shutdown and parking brake is set. On again when about to push back. 

 

 

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