Narrative:

On very short final to bur runway 7, I noticed a large error in my airspeed indication. My first officer was on his second line flight. On the ILS, inside the fap, we received a yellow 'caution' light for the 'rudder speed switch.' this warning occurs whenever there is a disagreement between the 2 rudder speed switches. These switches are set at 120 KIAS. I noted the caution, cancelled the alarm, and advised my first officer we would deal with it on the ground. Short final is no time to be looking up abnormal procedures. Normally this caution occurs when we are right on our approach speed of 120 KIAS. This caution is not unusual. Immediately after advising my first officer, I noticed my airspeed was steady at 140 KIAS. I mentioned the speed (140 KIAS) and that the caution usually came on at 120 KIAS. Throughout this my first officer never mentioned his airspeed. His airspeed was showing slightly below 120 KIAS. I called the 1000' check. Passing through decision ht plus 400, I reminded my first officer to 'call airspeed and altitudes.' passing through decision ht plus 300 he called vref+4. I glanced at my airspeed and saw vref+25. I questioned the airspeed and glanced at his airspeed indicator. I expected to find his airspeed reference bugs misset. Instead I found 2 wildly differing airspeed indications. I glanced up (it was supposed to be VFR) and saw the runway. Not knowing which airspeed indication to believe, I 'felt' the airplane to the runway. On shutdown my airspeed indication read 73 KIAS.

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Original NASA ASRS Text

Title: AIRSPEED INDICATORS IN COCKPIT OF LTT HAD 20 KT DIFFERENCE IN INDICATION. NOT NOTED UNTIL SHORT FINAL FOR LNDG.

Narrative: ON VERY SHORT FINAL TO BUR RWY 7, I NOTICED A LARGE ERROR IN MY AIRSPD INDICATION. MY F/O WAS ON HIS SECOND LINE FLT. ON THE ILS, INSIDE THE FAP, WE RECEIVED A YELLOW 'CAUTION' LIGHT FOR THE 'RUDDER SPD SWITCH.' THIS WARNING OCCURS WHENEVER THERE IS A DISAGREEMENT BTWN THE 2 RUDDER SPD SWITCHES. THESE SWITCHES ARE SET AT 120 KIAS. I NOTED THE CAUTION, CANCELLED THE ALARM, AND ADVISED MY F/O WE WOULD DEAL WITH IT ON THE GND. SHORT FINAL IS NO TIME TO BE LOOKING UP ABNORMAL PROCS. NORMALLY THIS CAUTION OCCURS WHEN WE ARE RIGHT ON OUR APCH SPD OF 120 KIAS. THIS CAUTION IS NOT UNUSUAL. IMMEDIATELY AFTER ADVISING MY F/O, I NOTICED MY AIRSPD WAS STEADY AT 140 KIAS. I MENTIONED THE SPD (140 KIAS) AND THAT THE CAUTION USUALLY CAME ON AT 120 KIAS. THROUGHOUT THIS MY F/O NEVER MENTIONED HIS AIRSPD. HIS AIRSPD WAS SHOWING SLIGHTLY BELOW 120 KIAS. I CALLED THE 1000' CHK. PASSING THROUGH DECISION HT PLUS 400, I REMINDED MY F/O TO 'CALL AIRSPD AND ALTS.' PASSING THROUGH DECISION HT PLUS 300 HE CALLED VREF+4. I GLANCED AT MY AIRSPD AND SAW VREF+25. I QUESTIONED THE AIRSPD AND GLANCED AT HIS AIRSPD INDICATOR. I EXPECTED TO FIND HIS AIRSPD REF BUGS MISSET. INSTEAD I FOUND 2 WILDLY DIFFERING AIRSPD INDICATIONS. I GLANCED UP (IT WAS SUPPOSED TO BE VFR) AND SAW THE RWY. NOT KNOWING WHICH AIRSPD INDICATION TO BELIEVE, I 'FELT' THE AIRPLANE TO THE RWY. ON SHUTDOWN MY AIRSPD INDICATION READ 73 KIAS.

Data retrieved from NASA's ASRS site as of August 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.