B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 205; Flight Crew Type 12500
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Incorrect / Not Installed / Unavailable Part
In the past several years; I have had a number of stuck open bleed valves when attempting a bleeds off takeoff. On this particular flight; the flight plan called for a bleeds off takeoff for payload with high temperature. We configured the bleeds per the supplemental checklist with the call for the before takeoff checklist. After number 2 BLEED was turned off; we noticed the R DUCT PRESS indicator remaining at 21 PSI. Having had this problem several times in the past; I coordinated with ATC for a gate return. While holding between runways; I sent an Electronic Logbook write-up and had First Officer (FO) call Operations and maintenance for gate return.After a 44-minute taxi; we arrived back at the gate. Maintenance said a minimum over one-hour delay; so we deplaned the customers. When consulting with maintenance they said they were able to get the valve to move after tapping it with a wrench. I suggested an engine run to make sure we don't have a potential repeat return to gate. All agreed. Engine run showed the same scenario I had at runway; (21 psi R DUCT PRESS). Maintenance suggested securing the bleed valve closed per MEL and flying to destination at FL250 or below. However; that wasn't possible with Cumuli Nimbus on our route with the potential of flying into icing conditions. Maintenance Control said it needed to be fixed/replaced. This resulted in a 7-hour delay waiting for a new aircraft inbound.Ordinarily; I wouldn't be writing a report over a ground maintenance issue; however; I think in this particular scenario; we may have a larger problem with the B737 engine bleed valves than meets the eye. The vast majority of our takeoffs are with BLEEDS ON. I don't know what the percentage of our bleeds off takeoff is; but I suspect it's in the low single digits. As a Line Check Airman; I've done more bleeds off takeoffs than the average pilot for demonstration purposes; which I suspect; is why I've had more of these write-ups in the last 5 years. I don't know what the exact percentage is of these failed bleed valves I've had; but depending on the time frame it's probably somewhere between 20 to 40 percent if not higher. My most recent one prior to this event was in June 2018; with the number 1 BLEED. In the last 2 months; I've done 3 bleeds off takeoffs; 2 of which resulted in gate returns and extended delays. I suspect a large number of these problems are being missed by our flight crews as they are moving switches and not checking the DUCT PRESS PSI. This was the case with my June flight. FO moved switches per the supplemental check list; however; didn't check the duct pressure before moving the APU BLEED switch to ON. I asked him to turn the APU Bleed OFF and check the L DUCT PRESS indicator. Sure enough; it was stuck between 15 to 18 psi. This was important as we were doing a required flight planned bleeds off take off using runway 02L (active runway was 20R at the time) so as to take the increased payload. The obvious threat here is being near the performance limits with decreased thrust due to a stuck open bleed. To add to that threat; what if the engine with the good bleed valve were to fail at or after V1 particularly in mountainous terrain. Another potential threat is a single engine taxi with the air conditioning panel pre-setup for a bleeds off takeoff per the Flight Manual; Normal 3.60.4. RT and LT PACK AUTO; ISOL VALVE CLOSE; No. 1 engine BLEED air switch OFF; APU BLEED air switch ON; No. 2 engine BLEED air switch ON. The threat here being after the delayed engine start of No. 1 engine; unless you moved the APU BLEED air switch momentarily to OFF to check L DUCT PRESS; you would never know if the number 1 engine bleed valve actually closed for a required BLEEDS OFF TAKEOFF. Also you have a potential dual bleed situation with no DUAL BLEED light indication because of the configuration of the switches. Then you have a BLEEDS OFF LANDING on occasion that need to be done to meet performance requirements. What are the potential ramifications should you lose an engine on a go-around right at minimums. This is a safety issue on many fronts that needs to be taken seriously. The vast majority of the times we do bleeds on takeoffs poses no threats to the takeoff performance or go-arounds for that matter. However; when looking through the QRH for other scenarios that require you to turn off the engine BLEED switch/switches brings up additional threats with a potential systemic problem on our B737 fleet. Here are the following QRH scenarios that require turning off the engine BLEED air switch/switches. WING BODY OVERHEAT; WING ANTI-ICE VALVE OPEN; ENGINE START - START VALVE OPEN; ONE ENGINE INOPERATIVE LANDING; DEICING/ANTI-ICING; UNPRESSURIZED LANDING PROCEDURE; UNPRESSURIZED TAKEOFF PROCEDURE.I hope this information helps. I look forward to your response and or any findings in this matter.
B737 Captain reported a 21 PSI indication in the manifold when the aircraft was configured for a 'NO BLEEDS' takeoff.