Narrative:

This is a human factors event caused from flying multiple aircraft types with different system. I recently completed training with airline on the B737-200 (1 week ago). The B737 has autothrottles which are engaged on takeoff and stay on under normal conditions until landing. At altitude, you engage the autothrottles to mach hold and leave them there. Upon completion of training at airline, I took some military leave to go through training on a new version of the B-1B. The B-1 recently received some new upgrades, one of which is an FMS. I was flying my first ride in this version after not having flown in approximately 6 weeks. There was a lot of 'heads down time' learning the new FMS. We had just completed some simulated bomb runs at altitude between hgo and laa 253039 and were heading down to tcc, NM. Having just flown the B737 on IOE and not flown the B-1, I was a bit rusty. The B-1 also has autothrottles but they are usually only used for maintaining a cruise speed. Anyway, I hooked up the autoplt in the 'altitude hold mode' which is 1 of 3 pitch modes (IAS hold and mach hold are the others, only 1 pitch mode can be engaged at once). To hook up the autothrottles in the B-1, you should press 'at engage.' on my flight, this was not lit. I acquired the speed I wanted, didn't see the correct button and hit 'mach hold' just like on the B737. The aircraft did exactly what I told it to -- mach hold versus altitude hold. Long story short -- we were heads down with the new FMS and descended about 400 ft low. ATC didn't say anything and I'm not sure they even noticed. Bottom line: if you are flying multiple aircraft types, be careful -- especially if you are more current in one than the other and watch the heads down time with FMS, etc.

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Original NASA ASRS Text

Title: A NEWLY TRAINED AIRLINE B737-200 FO, FLYING AS A B-1B RESERVE MIL PLT PIC, FAILS TO USE THE AUTOPLT FOR ALT HOLD FUNCTION AND ALLOWS THE ACFT TO SETTLE 400 FT LOW FROM ITS ASSIGNED ALT BEFORE CORRECTING BACK NEAR PUB, CO.

Narrative: THIS IS A HUMAN FACTORS EVENT CAUSED FROM FLYING MULTIPLE ACFT TYPES WITH DIFFERENT SYS. I RECENTLY COMPLETED TRAINING WITH AIRLINE ON THE B737-200 (1 WK AGO). THE B737 HAS AUTOTHROTTLES WHICH ARE ENGAGED ON TKOF AND STAY ON UNDER NORMAL CONDITIONS UNTIL LNDG. AT ALT, YOU ENGAGE THE AUTOTHROTTLES TO MACH HOLD AND LEAVE THEM THERE. UPON COMPLETION OF TRAINING AT AIRLINE, I TOOK SOME MIL LEAVE TO GO THROUGH TRAINING ON A NEW VERSION OF THE B-1B. THE B-1 RECENTLY RECEIVED SOME NEW UPGRADES, ONE OF WHICH IS AN FMS. I WAS FLYING MY FIRST RIDE IN THIS VERSION AFTER NOT HAVING FLOWN IN APPROX 6 WKS. THERE WAS A LOT OF 'HEADS DOWN TIME' LEARNING THE NEW FMS. WE HAD JUST COMPLETED SOME SIMULATED BOMB RUNS AT ALT BTWN HGO AND LAA 253039 AND WERE HDG DOWN TO TCC, NM. HAVING JUST FLOWN THE B737 ON IOE AND NOT FLOWN THE B-1, I WAS A BIT RUSTY. THE B-1 ALSO HAS AUTOTHROTTLES BUT THEY ARE USUALLY ONLY USED FOR MAINTAINING A CRUISE SPD. ANYWAY, I HOOKED UP THE AUTOPLT IN THE 'ALT HOLD MODE' WHICH IS 1 OF 3 PITCH MODES (IAS HOLD AND MACH HOLD ARE THE OTHERS, ONLY 1 PITCH MODE CAN BE ENGAGED AT ONCE). TO HOOK UP THE AUTOTHROTTLES IN THE B-1, YOU SHOULD PRESS 'AT ENGAGE.' ON MY FLT, THIS WAS NOT LIT. I ACQUIRED THE SPD I WANTED, DIDN'T SEE THE CORRECT BUTTON AND HIT 'MACH HOLD' JUST LIKE ON THE B737. THE ACFT DID EXACTLY WHAT I TOLD IT TO -- MACH HOLD VERSUS ALT HOLD. LONG STORY SHORT -- WE WERE HEADS DOWN WITH THE NEW FMS AND DSNDED ABOUT 400 FT LOW. ATC DIDN'T SAY ANYTHING AND I'M NOT SURE THEY EVEN NOTICED. BOTTOM LINE: IF YOU ARE FLYING MULTIPLE ACFT TYPES, BE CAREFUL -- ESPECIALLY IF YOU ARE MORE CURRENT IN ONE THAN THE OTHER AND WATCH THE HEADS DOWN TIME WITH FMS, ETC.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.