CL65 SLC-EUG AT CRUISE ALT HAD ELECTRONIC INTERFERENCE WITH EICAS SYS. ON DSCNT TO EUG EXPERIENCED AIRSPD DEV BTWN CAPT AND FO. HAD CABIN ATTENDANT CHK FOR ELECTRONIC DEVICES USE AND HAD THEM TURNED OFF. BAL FLT NORMAL.

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FLT FROM SLC TO EUG BEGAN AS JUST ANOTHER ROUTINE FLT. BEGINNING WITH THE PUSHBACK; TKOF; AND CLBOUT; THE FLT WAS PROGRESSING NORMALLY. ONCE WE CLBED THROUGH 10000 FT; THE FO PERFORMED THE APPROPRIATE CHKLIST AND NOTIFIED THE FLT ATTENDANT THAT IT WAS SAFE TO BEGIN CABIN SVC. THE FLT ATTENDANT NORMALLY MAKES HER CABIN BRIEFING INFORMING THE PAX THAT THE USE OF PORTABLE ELECTRONIC DEVICES IS NOW ALLOWED. ROUGHLY 5-10 MINS LATER; WE OBSERVED A CAUTION MESSAGE ON OUR EICAS DISPLAY INDICATING AN 'EFIS COMP MON.' THIS PARTICULAR MESSAGE IS DISPLAYED ANY TIME THERE IS DISAGREEMENT BTWN THE CAPT'S AND THE FO'S FLT INSTS. IN THIS CASE WE HAD A DISAGREEMENT OF HDG INDICATORS. AFTER FOLLOWING OUR QRH; THE MESSAGE STILL REMAINED. AFTER XCHKING THE STANDBY INSTS; IT WAS DETERMINED THAT THE FO'S HDG WAS THE MOST ACCURATE. THE QRH NOW DIRECTS THE CREW TO SELECT ATTITUDE AND HDG #1 OR #2 ON THE SOURCE SELECT PANEL; WHICHEVER HAS BEEN DETERMINED TO BE MORE ACCURATE. WX CONDITIONS AT THE TIME WAS SMOOTH AIR AND ON TOP OF AN OVCST. FINALLY WE REACH OUR FINAL ALT OF FL330 AND FOR THE NEXT HR THE FLT WAS UNEVENTFUL. SOMEWHERE AROUND 150 MI E OF EUG; ZSE GAVE US A PLT'S DISCRETION DSCNT TO FL240. I ELECTED TO BEGIN THE DSCNT TO TRY TO GET OUT OF THE STRONG HEADWINDS WE'D BEEN FIGHTING MOST OF THE WAY. AS THE ACFT APCHED THE DSCNT PROFILE SPD OF 320 KTS; THE EICAS DISPLAYED ANOTHER 'EFIS COMP MON' CAUTION MESSAGE. THIS TIME THE PROB WAS WITH A DIFFERENCE IN OUR AIRSPD INDICATORS. MINE WAS READING 310 KTS AND THE FO'S WAS READING 320 KTS. I AGAIN HAD THE FO REFER TO QRH TO CORRECT OUR PROB. BUT BEFORE HE COULD COMPLETE THE FIRST FEW ITEMS; THE PROB HAD CORRECTED ITSELF. MINS LATER THE 'EFIS COMP MON' APPEARED A THIRD TIME. THIS ONE WAS CAUTIONING US ON AN ALTIMETER DIFFERENCE. AS USUAL; WE PULLED OUT THE QRH; BUT BEFORE IT COULD BE READ; THE DISCREPANCY IN AIRSPD INDICATORS HAD ONCE AGAIN APPEARED. ONCE ALL OF THE PROB MESSAGES HAD STOPPED BLINKING ON AND OFF; WE WERE ABLE TO BEGIN THE APPROPRIATE QRH ITEMS. THESE ITEMS INCLUDE XCHKING THE STANDBY INSTS AND DETERMINING THE RELIABLE AIR DATA SOURCE (#1 AND #2). AGAIN THE FO'S INSTS WERE THE RELIABLE SOURCE. AFTER ALL CHKLISTS WERE COMPLETED; THE FO ASKED 'YOU DON'T SUPPOSE THIS COULD BE CAUSED BY THE PAX USING COMPUTERS OR CD PLAYERS?' MY FIRST THOUGHT WAS NO; ONLY BECAUSE I'VE NEVER HAD ANY PROBS LIKE THIS IN THE PAST. BUT AT THIS POINT; I WAS OPEN TO ANY SUGGESTIONS. THE FO THEN CALLED BACK TO THE FLT ATTENDANT AND ASKED IF THERE WERE ANY PORTABLE ELECTRONIC DEVICES IN USE IN THE CABIN. SHE SAID SHE WOULD CHK AND GET BACK TO US. AS IT TURNED OUT; THERE WERE 6 CD PLAYERS AND 1 LAPTOP COMPUTER IN USE AT THAT TIME. AS WE WERE STILL ABOVE 10000 FT; THE FLT ATTENDANT HAD NOT HAD A CHANCE TO MAKE HER CABIN BRIEFING REGARDING DISCONTINUATION OF ELECTRONIC DEVICES. THE FLT ATTENDANT AT THIS TIME WAS INSTRUCTED TO MAKE HER BRIEFING AND TO ENSURE THAT ALL PORTABLE ELECTRONIC DEVICES WERE IN THE OFF POS. THE FLT ATTENDANT THEN RPTED BACK TO INFORM US THAT ALL SUCH ITEMS WERE OFF. JUST TO SEE IF THIS WAS THE CAUSE OF SOME; ALL; OR NONE OF OUR PROBS; I ELECTED TO PLACE ALL OF THE SOURCE SELECT SWITCHES BACK TO THEIR NORMAL POS. WITHIN ABOUT 1 MIN; MY AIR DATA COMPUTER WAS WORKING AND SHORTLY AFTER THAT MY 'AHRS' REALIGNED TO THE APPROPRIATE HDG. THE FLT CONTINUED TO EUG WITHOUT FURTHER INCIDENT. ONCE WE ARRIVED; I ADVISED THE NEXT CREW OF WHAT HAD HAPPENED AND TO BE AWARE OF ANY ABNORMAL INDICATIONS. I ALSO ASKED THEM TO LET ME KNOW IF THEY HAD ANY OF THESE TYPE OF PROBS ON THE WAY BACK TO SLC. THE NEXT DAY THE CAPT WHO TOOK THE ACFT SAID HE HAD IT FOR THE REST OF THE DAY AND HAD NO PROBS AT ALL.