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ATA36 BLEED PRESS VAR during MES

PostPosted: 21 Nov 2016, 04:57
by Pepa80
Hi Gents, we are facing problem 737NG : DURING ENG 2 START SUDDEN PX DROPS FROM 38PSI TO 15PSI IN BOTH BLEED DUCTS WHEN ISOL VLV OPN, WHILST ONLY IN LH BLEED DUCT WHEN ISOL VLV CLSD. - BLEED PX DROP LASTS 2-3 SECS WITH ALMOST REGULAR INT 10-15 SECS - BLEED PX DROPS ACCOMPAINED WITH AUDIABLE BANG EFFECT, SOURCE OF THIS BANG IS ALL ALONG APU BLEED DUCT. - APU INPUT MONITORING DATA THROUGH CDU -MES SWITCH 1 (NO CHANGE DURING PHENOMENA), IGV POSITION AROUND 90 DEG`S, SCV POSITION > 90 DEG`S AFTER PX DROP TO 30 DEG`S THEN AGAIN > 90 DEG`S (LOOKS MORE OR LESS LIKE APU COMP PROT THAN ROOT CAUSE, AS THIS PHENOMENA OCCURES ONLY DURING ENG 1 START) - BLEED PX DROPS OCCURED ONLY DURING MES ENG 1, IRRESPECTIVE BLD ISOL VLV SW POS. PRSOV, WTAI PHYSICALLY CHECKED CLSD, APU BLEED VLV OPN, ENG 1 START VLV OPN DURING THIS PHENOMENA, APU SCV OPENS AFTER LOUD BANG, APU ALREADY REPLACED - NO EFFECT...

Re: ATA36 BLEED PRESS VAR during MES

PostPosted: 27 Nov 2016, 15:25
by sjap
Check your PRSOV reverse flow protection and check the 5th stage checkvalve it could be jammed open. It happend before.
Ty to open the start valve cb and then put eng start sw in GND, your APU bleed should rise to 35-40 PSI for MES while startvalve stays close. (you fool the system) If it doesnt continue with T/S on your start switch signal for MES.

Re: ATA36 BLEED PRESS VAR during MES

PostPosted: 28 Nov 2016, 16:06
by Pepa80
Thank You Jean-Paul for advice! Unfortunately or fortunately (depends on the point of view) the related aircraft moved to another station...