747-8 HYD PR Flickering on STAT

[Tiberione 3]

I noticed during pre-flight, when I switched to STAT monitor my APU startup, that HYD PR on 1,2,3 were all flickering 0-100. HYRD PR on 4 was constant as 4 was set to AUX, 1,2,3 were set to OFF.

Is this normal? Let me know if I need to provide any more info.

https://i.gyazo.com/8dc5d8345063af201cc39f023a7bfe8d.mp4

 

Edited October 15, 2018 by Tiberione

[downscc 1,327]

This is normal for both 744 and 748.  A more interesting question is why this occurs.

[LRBS 944]

NO NO NO nothing is normal about it, they don't flicker at all, especially as is on this movie clip.

As a note per SOP we turn HDP4 and HDP1  to AUX before engine start not while APU is starting as you  indicating.

Please read the manual carefully and follow whatever SOP you have.

 

 

[Tiberione 3]

30 minutes ago, killthespam said:

NO NO NO nothing is normal about it, they don't flicker at all, especially as is on this movie clip.

As a note per SOP we turn HDP4 and HDP1  to AUX before engine start not while APU is starting as you  indicating.

Please read the manual carefully and follow whatever SOP you have.

 

 

Thanks for the heads up - I missed the "1," in the checklist I have! This was right before pushback/start, just starting the APU to move away from gate. Good to know for the future though!

 

Curious what caused this flickering. Once I moved all pumps to AUTO, they pressurized to ~3000 and flickering stopped. Ill check again when I land to see if the flickering continues after shutdown.

[downscc 1,327]

yeah, I didn't read the original post close enough.  The flickering hyd press values when all pressurization is removed is normal.  The B744 does it and the 748 as well.

[LRBS 944]

Dan, I wished I had money in my pocket now for how many times  I didn't read a original post close enough ;-))

[Michael Moe 494]

On 10/15/2018 at 9:16 PM, downscc said:

This is normal for both 744 and 748.  A more interesting question is why this occurs.

Can you help with that ? Learning is always fun 😎

 

Thanks

Michael Moe

[downscc 1,327]

6 hours ago, Michael Moe said:

Can you help with that ? Learning is always fun 😎

 

Thanks

Michael Moe

Thank you Michael.  The hydraulic pressure sensors use transmitters to convey pressure information in the form of a 4 - 20 mA signal, which is a standard analog signal throughout industry.  The use of 4 - 20 mA signal is preferred to a voltage signal because noise takes the form of small voltage spikes that a current sensor will reject.  Schema vary, but say for example 4 mA is the lowest end of the calibration scale and that is 100 psi and 20 mA represents 3100 psi.  When the power is removed from the transmitter and the value is zero mA then this is outside the calibration range and the indication will be that of noise down around 100 psi.

Edited October 17, 2018 by downscc

[Michael Moe 494]

1 hour ago, downscc said:

Thank you Michael.  The hydraulic pressure sensors use transmitters to convey pressure information in the form of a 4 - 20 mA signal, which is a standard analog signal throughout industry.  The use of 4 - 20 mA signal is preferred to a voltage signal because noise takes the form of small voltage spikes that a current sensor will reject.  Schema vary, but say for example 4 mA is the lowest end of the calibration scale and that is 100 psi and 20 mA represents 3100 psi.  When the power is removed from the transmitter and the value is zero mA then this is outside the calibration range and the indication will be that of noise down around 100 psi.

Thanks :-) We have a lot of 4-20mA in my business so makes sense. 

Apreciated 

Michael Moe