THE CAPT HEARD THE CTLR SAY 'MAINTAIN 4000 FT UNTIL ESTABLISHED ON THE ILS AND CLRED FOR THE ILS APCH RWY 21.' THE RPTR; THE FO FLYING HEARD THE CAPT READ BACK 4000 FT. THE CTLR SEEING THE FLC DSND THROUGH 4500 SAID THEY WERE TO MAINTAIN 5000 FT. THE RPTR SAID THEY HEARD 4000 FT AND READ BACK 4000 FT BUT WERE CLBING BACK TO 5000 FT. THE ILS WAS COMPLETED WITH NO FURTHER PROBS.

Narrative

ON THE FLT FROM GTF TO GEG IT WAS MY LEG AND THE CAPT WAS WORKING THE RADIOS. WE WERE GETTING VECTORED TO INTERCEPT THE ILS INBOUND AND THE GS INTERCEPT ALT IS 4000 FT MSL. WE WERE USING ILS RWY 21. IN THE PREVIOUS 1500 FT THE NOSE GEAR STARTED CYCLING BY ITSELF; AND I WAS PREOCCUPIED WITH THAT PROB WHEN ATC GAVE US THE HEADING TO INTERCEPT THE ILS AND MAINTAIN 5000 FT UNTIL ESTABLISHED AND CLRED FOR THE APCH. I DID NOT HEAR THE ALT BUT DID HEAR THAT WE WERE CLRED FOR THE APCH AND DID HEAR CAPT READ BACK MAINTAIN 4000 FT AND CLRED FOR THE APCH AND THE CAPT SET 4000 FT IN THE ALT ALERTER. WE WERE GOING THROUGH THE LNDG CHKLIST; INTERCEPTING THE ILS AND DSNDING THROUGH 4500 FT WHEN ATC SAID THAT WE WERE TO MAINTAIN 5000 FT. THE CAPT TOLD ATC HE READ BACK 4000 FT; WHILE I CLBED BACK TO 5000 FT AND INTERCEPTED THE GS AND FLEW IT DOWN TO LNDG. THE THING THAT I COULD OF DONE DIFFERENT IS CHALLENGED THE CAPT SINCE I DID NOT HEAR THE ALT MYSELF OR ASK ATC TO CONFIRM IT OR ASK THE CAPT TO ASK ATC TO CONFIRM THE ALT.