A B737-800 CAPT WAS MAKING IN-RANGE CALLS WHILE LETTING HIS FO HANDLE THE FLYING AND COMMUNICATING. THEY ENDED UP 10000 FT ABOVE THEIR XING RESTR BECAUSE THE FO COULD NOT FIGURE OUT HOW TO USE THE FMS.

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ON THE CUGAR 6 ARR TO IAH IN A NEW GENERATION B737-800; WE WERE GIVEN DIRECT HOAGI TO CROSS AT 10000 FT AT 250 KTS. IT WAS THE COPLT'S LEG AND I HAD GIVEN CTL OF THE ATC RADIO AND THE AIRPLANE TO THE COPLT WHILE I MADE SEVERAL IN-RANGE CALLS TO THE COMPANY AND MAINT. I ALSO DID A PA. WHEN I RETURNED TO FLYING IT APPEARED THAT THE COPLT WAS HAVING A HARD TIME WITH THE PATH DSCNT. THE AIRPLANE HAD OVERSPED AND THE VNAV HAD REVERTED TO LEVEL CHANGE. HE WAS GOING HIGHER ON THE PATH SO I TOLD HIM HE NEEDED TO GET BACK ON THE PATH. ABOUT THAT TIME WE WERE HANDED FROM CTR TO APCH AND I WAS SHOCKED TO FIND US AT FL200! WE WERE 10000 FT HIGH ON THE XING RESTR. MY EMOTIONS RAN FROM DISBELIEF TO ANGER. I TOLD THE APCH CTLR WE NEEDED TO BREAK OFF THE ARR AND HE HANDED ME BACK TO CTR WHO VECTORED US UNTIL WE GOT TO 10000 FT AT HOAGI. WE LANDED WITHOUT INCIDENT AND THE CTLRS DID NOT HAVE A PHONE NUMBER TO CALL. THE COPLT AND I SPENT A LONG TIME TRYING TO FIGURE OUT WHAT HAPPENED. THE COPLT WANTED TO DO A NEW RNAV APCH TO RWY 26 WHICH HE BUILT IN THE FMS AND WE BRIEFED IN DETAIL. SOMETIME IN THERE; THE XING RESTR AT HOAGI GOT DELETED. THE COMPUTER BUILT A DSCNT PATH BASED ON AN APCH FIX AND NEITHER OF US CAUGHT IT. WE FOCUSED ON THE PATH SO INTENTLY THAT OUR ATTN WAS ON GETTING AND STAYING ON THE PATH EVEN THOUGH THE PATH WAS WRONG. I FELT ESPECIALLY BAD BECAUSE I AM A LINE CHK AIRMAN AND I AM SUPPOSEDLY AN EXPERT ON THE NEXT GENERATION AIRPLANE. FOR WHAT IT'S WORTH; I HAVE ALWAYS THOUGHT THE MOST DANGEROUS PART OF A FLT IS WHEN THE OTHER PLT IS OFF THE RADIO DOING 'COMPANY' DUTIES.