B757-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft
[In] cruise flight at FL390; we experienced a total loss of cabin pressurization. [We] diverted into [a suitable alternate]. We were given vectors to lose altitude towards the east and vectored to the left back around to the west towards [the] airport.Events leading up to this were as follows. The right engine bleed light illuminated overhead as the EICAS message did along with the aural and visual CAUTION (amber) level alerting system. The aural portion was silenced. The R pneumatic duct pressure indicated losing pressure slowly while fluctuating. The left one seemed OK at the moment. So we opened up the QRH checklist. It seemed as though the right engine bleed light OFF EICAS was the appropriate choice in this case. It essentially had told us to turn off the R engine bleed switch and turn off the associated R pack selector. We did this. We decided to reset the bleed air switch once with the associated pack selector turned off in an attempt to regain that system's side and to preclude or prevent losing cabin pressurization. As that system's side was reset things appeared to be normal for a shorter period of time. Then the left engine bleed VALVE light (I believe) EICAS appeared. The RIGHT duct pressure started to decrease rather rapidly; and the LEFT DUCT pressure stayed abnormally higher. That accompanied again with both engine bleed lights overhead with the associated off switches lights. It was apparent that we would now lose [pressurization] since cabin altitude warning horn and light also displayed on the EICAS. It was most likely apparent the cabin pressurization loss and we would have to commence a rapid descent to some lower altitude while wearing our oxygen masks. Say a minimum of 10;000 feet. At this point the terrain was not an issue. My first officer continue to fly the aircraft as I had designated him the pilot flying; and I elected to be the PM and have a look at the QRH checklist. He had things under control with the flying. He was doing a very good job and his awareness level was high. I; as the PM was very busy trying to run the other checklists with regard to landing preparation such as the In Range checklist and the approach checklist. Of course; setting up for the appropriate runway with the ILS back up with a visual approach and landing. The weather was quite good. Some gusty winds from the southwest about 20 kts. The emergency vehicles were awaiting our landing which I didn't ask for; but if that's their policy; fine. They asked if we needed any further assistance. I had said no and we were cleared to the ramp. Upon parking at the gate; the local airport police boarded our airplane and asked us to see our FAA pilot certificates and current FAA airmen medicals. This part was just a very cordial and cooperative conversation. I then proceeded to make the AML write up in conjunction with the local aircraft maintenance tech. The previous AML historical write up was pretty much the same thing that was happening to us here now. A total loss of cabin pressurization due to a similar if not identical problem that has not been resolved as of yet; perhaps at least once before. As we had noticed earlier that the previous crew had done essentially the same thing as they had regained cabin pressurization by 15;000 feet. I think that is what led me and my first officer to conclude in an attempt to reset the initial right malfunctioning bleed system on the right engine. Although the QRH did not call for that. I called the duty officer after parking and shutdown. I explained to him the reason for the divert and the emergency situation. He had already been aware of it. Things were quite busy to notify the company during the divert; so I had ARTCC notify [Company] as to what was happening. I believe that they did. Knowing that there was a previous AML write for a very similar or identical problem; clearly more troubleshooting needs to be done to identify the suspect pneumatic system related parts. So to answer the question; I don't know what caused the problem. We just reacted to it methodically; and tried to follow procedures the best we could. Also; in the safest manner that we could. All the while considering the effect on the company's operations. Sometimes troubleshooting airplanes is not an easy task; and can be an arduous one. I'm not here to cast any blame on anyone person or group. Unfortunately; with human factors; procedures and what not; it takes a while to troubleshoot something accurately and it may take more than one occasion or occurrence. The total loss of cabin pressurization; while urgent; is not a worst-case scenario as compared to other things. Particularly when you have a F/O who's doing a very good job flying; and has a higher awareness level. And; of course really good weather and more optimal conditions. i.e. daylight flying; flat terrain; excellent VMC weather; etc... In summary; I think that it might be a wiser move NOT to trouble shoot outside of the QRH. Sometimes this can amplify an issue. Although; since I had felt well prepared for this a/c's history with pressurization issues; we discussed this and a possible plan should we encounter a loss of cabin pressure. One was a discussion of attempting one reset to maintain or recover it. Looking back; there's really nothing that needs to be done too quickly; except putting on the O2 mask and breathing oxygen while establishing positive understandable communications.
[Report narrative contained no additional information.]
B757-200 flight crew reported diverting to a nearby alternate after losing cabin pressure.