Large Transport
Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 88; Flight Crew Total 6400; Flight Crew Type 1270
Situational Awareness; Fatigue; Communication Breakdown; Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Weather / Turbulence
General None Reported / Taken
Human Factors; Weather
On descent to the Guam airport we flew an approach into Guam for a landing on 24R. We began the final descent phase to the runway with weather which was above minimums. During the approach we encountered moderate turbulence and heavy rain. Upon reaching the MDA crew communications were somewhat hindered due to the extremely loud impacts of rain on the windshield. As a result of confusion and coordination we inadvertently descended below the MDA (while a non-flying crewmember was yelling altitudes AGL in the back of the cockpit); upon realizing this we also noticed the runway in sight ahead of us and being in this position with a clear descent path to the runway after executing a small correction to the left. The Captain and I elected to continue to a landing. We landed approximately 3000 feet down the runway at the very end of the touchdown zone.The problem was most likely caused by fatigue (extremely long day and wake cycle including an earlier diversion); flying a non-precision approach in marginal weather; inability to communicate clearly due to the loud environment within the cockpit; and confusion caused by other individuals (ACM) interfering with communications between pilots flying the aircraft.
Large transport First Officer reported descending below charted altitude on a non-precision approach to GUM in heavy rain.