B747-400
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Distraction; Human-Machine Interface; Training / Qualification
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Company Policy; Human Factors; Procedure
On arrival into EDFH we were issued the NDB 03 approach at which point we set the aircraft up to perform an RNAV approach as the NDB 03 was not in the database. We were issued a final heading to intercept the inbound course and cleared to descend to 5;000 FT. The FAF; 'LULIS;' [is to be crossed] at or above 5;000 FT. We intercepted the final approach course about five miles outside of LULIS at 5;000 FT at which time I selected 2;100 on the MCP as this was the MDA. I then selected FLCH instead of VNAV which caused the aircraft to descend below the 5;000 foot restriction at LULIS. At approximately 4;200 FT I realized my error and increased power to arrest the descent and climb back to 5;000 FT. At this point the Tower questioned our altitude and asked us to return to 5;000 FT. I climbed to about 4;800 FT by the time we passed LULIS and intercepted the glide path with no further events.
Planned to fly the NDB 03 using an ILS overlay and LNAV/VNAV. [Crossing at] LULIS; per the approach plate; is 5;000 FT with a descent to FAF altitude inside LULIS. The First Officer (pilot flying) executed correct procedures for the approach up to the point of selection VNAV; at which point he selected FLCH (pilot flying had already selected DA/H in the altitude window as we were cleared for the approach).As pilot not flying; I allowed myself to be distracted with configuring the aircraft and radio calls and failed to immediately recognize the error. Through peripheral vision; I knew he'd selected something and I assumed it was VNAV. For procedures normally not often executed (I.e.; LNAV/VNAV approach); [we should] emphasize verbal communication between crew members to include a brief step-by-step outline of each event and when it will happen (example; 'I'm going to insure LNAV is selected; then when cleared for the approach I'll set the DA(H) in the altitude window; set my speed; then select VNAV'). This can also be verbalized as each step is completed.
A B747-400 flight crew level at 5;000 MSL and approaching the FAF while performing an autoflight conducted RNAV overlay approach to a published NDB IAP inadvertently selected FLCH (Flight Level Change) mode vice VNAV after setting the MDA (451 AGL) prior to crossing the FAF at the charted 5;000 MSL. As a result; the aircraft immediately began a descent below their cleared altitude. A Relief Pilot in a jumpseat and the Tower Controller provided alerts after a descent of about 800 FT.