SPD DETERIORATED ON CLB WHEN PF; CAPT; INCREASED CLB RATE TO MAKE XING RESTR. FO; WHO WAS 'HEAD DOWN' LOADING A WAYPOINT FELT ACFT VIBRATION AND LOOKED AT INSTS JUST AS CAPT WAS ADDING PWR AND LOWERING NOSE.

Narrative

WHILE CLBING THROUGH FL250 FOR FL290 THE ACFT LOSS IAS AND STARTED TO APCH A STALL CONDITION AS THE ACFT WAS BANKED IN A TURN. JUST PRIOR ATC CLRED OUR FLT DIRECT TO A WAYPOINT THAT WAS NOT LOADED INTO THE INS'S (INERTIAL NAV SYS). BEING THE PNF; I WAS ASKED BY THE CAPT TO LOAD THE NEW WAYPOINT INTO THE 3 INS UNITS. THE PLT FLYING HAD REDUCED IAS TO 290 KTS IN ORDER TO INCREASE THE RATE OF CLB TO MEET A XING RESTR. THE SO HAD THE MASTER FLT PLAN WHICH I NEEDED TO GET THE LATITUDE/LONGITUDE TO PUT INTO THE INS UNITS. I RETRIEVED THE FLT PLAN AND INSERTED THE LATITUDE/LONGITUDE INTO THE INS UNITS. THIS PROC TOOK ABOUT 1 1/2 MINS. AT THIS TIME I FELT A VIBRATION BEGINNING IN THE ACFT. I LOOKED TO THE FLT INSTS AND NOTICED THAT THE IAS HAD DECREASED TO ABOUT 250 KTS AND THE CAPT (PF) WAS INCREASING THRUST TO THE ENGS AND DECREASING THE PITCH ATTITUDE OF THE ACFT. THE ALT OF THE ACFT DSNDED FROM FL249 TO FL244. I CALLED ATC AND ADVISED THE CTLR OF THIS AND SAID THAT WE WERE NOW CLBING TO FL290.