4:50 PM , 1 Comments

Work related:

Today while departing an aircraft (737NG), there was a defect.
A defect which is not reflected in the FIM.

There was a beeping sound coming from the cockpit speakers, both speakers to be exact.
At first I thought it was some PTT transmission hard on, but after disconnecting all the headsets, handmics. oxy masks, the sound is still there!

We tried replacing a new REU, nil fix.
Replaced  both ACPs, Nil Fix.
Referred to FIM, WDM, SSM...

Tried changing power source from ground power to Apu gen power (there was a SPCU fault before this..) , Nil fix.

The only thing that can silent the speakers were switching BOTH Acp altn/norm switch to Alternate, and tripping all interphones CBs.

I also tried inspecting all service interphone jacks and cleaned all jacks and cycled with a headset, nil fix.

After many attempts, KS came to the rescue, he tripped every single CB from P6, to P18 one by one.
Finally after TCAS CB tripped, the sound went off, we immediately know that's the problem!

Did a TCAS test and it failed.
Replaced a new TCAS processor and ops test satis.

The weird sound disappeared!!!

This was a hard troubleshooting for me, thankfully there was someone to help me at the very end at 10pm!
The sound probably was caused by a defect of the TCAS processor hence transmitting nuisance sound through the speaker.

Thank you KS.

Good experience for me.

If any of you have experienced this before, feel free to email me at

Thank you for reading.