B737 Next Generation Undifferentiated
Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 155; Flight Crew Total 8500; Flight Crew Type 452
Troubleshooting; Human-Machine Interface; Fatigue; Distraction; Confusion; Communication Breakdown; Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Company Policy; Human Factors
During preflight the FMS would not accept initialization from the ACARS; requiring me to manually enter all data. The route; however; did autoload. Strange equipment notifications [enroute] prompted a call to Dispatch concerning whether or not the aircraft was reporting its position; it wasn't. I now had a slight doubtful feeling concerning system functionality. ZZZ Airport was reporting approximately 400/1 mist/drizzle. We briefed ILS PRM XL approach. All checklists were accomplished well in advance of approach and we were descending in level change mode when we were cleared for the ILS. I tried to accomplish the [company directed mental reminder procedure or 'mnemonic'] 'down to the line' (to assure appropriate Lateral/Altitude/Vertical Navigation Mode/Speed intervention configurations) but we were below 4;000 FT and when I tried to do so this VNAV didn't engage.  We both looked at the approach and noted that VNAV wouldn't work since the intermediate fix (prior to ZZZZZ Intersection) had an altitude of 4;000 FT which we were already below. I then selected APP; we both acknowledged approach mode and I saw the white glideslope armed [indication]; we had previously intercepted the LOC [to satisfy] the 'Lateral Nav' portion of the mnemonic procedure. Approaching ZZZZZ Intersection something didn't feel right and I started re-checking/cross checking the MCP when the 'LOW Altitude' alert was issued by ATC. We accomplished a missed approach at this point. The next approach went just fine.
The First Officer advised he now believes the FMS anomalies addressed in the beginning of his report were not a factor in the eventual CFTT event although; at the time of the event; they had cast a pall of mental skepticism that compounded efforts to understand what was taking place when certain modes failed to engage as expected. He believed the mental distractions were complicit in his failure to scan raw data that would have illuminated their predicament.The reporter expanded on his comments regarding the company SOP mnemonic utilized to insure autoflight compliance with the lateral and vertical paths; airspeed and altitude constraints of an IAP. In particular; in this instance; to assure compliance with step down fixes prior to glideslope intercept using VNAV. Specifically the mnemonic requires the flight crew to assure: Lateral track compliance armed or active via VOR/LOC; altitude alert initially set to field elevation +100 FT to allow VNAV to comply with any procedural altitude restrictions prior to the FAF/glipeslope intercept altitude (but is subsequently reset to the MAP altitude at glideslope intercept/FAF passing); the appropriate vertical nav (VNAV) mode is engaged; and; airspeed window is set per aircraft configuration and vertical path mode.The reporter clarified that the approach clearance from ATC was 'cleared for the ILS approach; descend and maintain 3;000 FT until established.' At that point; 3;000 FT was selected in the altitude alert window; VOR/LOC was armed and; shortly; went active. Shortly after LOC was active they reset the altitude alert to field elevation +100 FT per the mnemonic.At the time FE+100 was set 4.5NM from ZZZZZ Intersection; the glideslope intercept fix; was the active waypoint and had a published and programmed crossing restriction of 4;000 MSL. When the First Officer attempted to engage VNAV; however; they were already below 4;000 FT on their way to their cleared altitude of 3;000 FT MSL; thus VNAV would not engage and the FMS vertical mode remained in LVL CHG and; as previously configured; the jet obediently continued its descent toward field elevation +100 FT with the throttles at idle.The reporter; when he started not 'feeling' right and was reviewing the MCP (Mode Control Panel); also noted the full scale low deflection of the raw data glideslope signal and concurrent with the Low Altitude Alert warning from ATC initiated the go-around.
The flight was an all nighter. The weather approximately 400/1; drizzle and mist. The approach was properly briefed; and all checklists complied with. I was the pilot not flying; the First Officer was the pilot flying. The First Officer had selected 'Level Change' while descending.When cleared for the approach; he accomplished [the SOP mental reminder mnemonic]; but VNAV would not engage when selected. Approach mode was then selected although; looking back at it; the switch was not illuminated (the illumination turns off when the approach mode engages). When I switched to Tower at ZZZZZ Intersection; we were told they had a low altitude alert. Not immediately seeing the problem; we elected to go-around. Looking at the flight director; both needles were centered. I simply had not looked at how the approach had been set up on the MCP close enough. The First Officer later told me that the level change mode had remained selected; which explains why everything was centered and the aircraft was dutifully descending to the selected altitude of field elevation per the [mnemonic] check. We executed a missed approach; and the next approach was perfect.This is the first red-eye I had flown. While I do not wish to say I was fatigued; I definitely had been without sleep for close to 24 hours. I simply could not get to sleep during the day; and had been up since about XA:30 AM EDT. Sleeping during the day seems to be difficult for me; and lack of sleep certainly had an impact on how well I was performing (or not performing) my duties as PM; although I did not feel at all sleepy at the time; nor did I feel fatigued. I will surely attempt to avoid all red-eyes in the future.One thing I will include on all approaches in the future is a mental or verbal verification of the final approach fix crossing altitude at the time of crossing. I cannot believe we both missed something so obvious; but we did.
A B737NG being vectored for an ILS; failed to level at 3;000 FT until established; as cleared. When a low altitude alert sounded the Approach Controller; no longer able to contact the flight; promptly called the Tower who advised they had done; so and directed a go-around as the flight was passing 1;400-1;600 FT MSL (400-600 FT AGL) and continuing their descent while still one mile outside the FAF/glideslope intercept altitude of 2;900 FT MSL. Difficulty in utilizing a company directed memory aid intended to insure proper autoflight configuration and a resulting improperly set altitude alert at field elevation +100 FT likely contributed.