Date: 201306
Local time of day: 0601-1200
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Weather elements / visibility: Thunderstorm
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
ATC / advisory: Tower ZZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Relief Pilot; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Time Pressure; Other / Unknown
Second reporter function: Pilot Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Declared Emergency
Contributing factors: Aircraft; Human Factors; Procedure; Weather
Primary problem: Ambiguous

Narrative: After a divert from Beijing then an alternate closing; we proceeded to the next suitable airport. Initially we were assigned to Runway 15 and after Tower offered Runway 33; we switched to the VOR Runway 33 approach. Fully configured at the FAF; the aircraft pitched over seemingly more than normal; but due to fatigue I did not notice the VSI. I was however; monitoring the altitude. I was not aware of the descent rate or that the aircraft had descended below MDA. We had sighted the runway off to our right and a turn was made to intercept final aways out. We had briefed a PAPI and saw we were below a normal glide path and I diverted my attention to monitoring altitude to make sure at that point no further descent was allowed. I assumed that the MDA was still set in the window and another cockpit crew member said the MDA of 650 was still in the window upon landing.


Second narrative: On arriving to a foreign airport we found the airport weather was good but the arrival corridor had heavy showers and it appeared to have thunderstorms along the way. Our alternate weather was good and we flew over it on our only attempt to see if we could go around the weather. From this flyover; we could see that the heavy weather was well northwest of the alternate. Prior to starting the arrival; we chose to set a BINGO 2K [divert fuel] higher than our R plus A [reserve plus alternate]. We ended up choosing to divert prior to reaching this fuel amount. We said we wished to divert to our alternate and every time we were told we could NOT go there and for us to state intentions. After many attempts; we chose ZZZZ which had good weather. ZZZZ was landing south; but from our arrival direction; landing north was closer. Prior to arriving at ZZZZ we declared an emergency. I was preparing for the ILS landing south when the Controller offered the VOR landing north. Since this was closer; I accepted. We set the VOR in the FMC; checked the iPad and confirmed an altitude of 600 plus 50 for MDA 650 RNAV approach. The aircraft was quickly configured; LNAV; VNAV; MDA (DA); and airspeed were all set. The PFD confirmed LNAV and VNAV PATH were engaged. We NEVER saw the DIAMOND on the Nav Display but the autopilot was engaged and at the FAF the aircraft pitched over but at a higher rate than I expected. Weather was good enough to make easy ground contact visually and we were still above the adjusted MDA. When I saw the approach lights and PAPI; I had to make an adjustment for runway alignment and leveled off as I saw that I was low. After a brief altitude adjustment; I saw RED over WHITE and continued to a landing. We landed and taxied off the runway.


Synopsis: Air Carrier flight crew reports diverting to a second alternate after their filed alternate and original destination are denied by ATC due to weather. During the non-precision approach the aircraft descends below MDA prior to arriving at the normal glide path. An emergency is declared during the diversion due to fuel and the aircraft lands with seven thousand pounds.