A B757-200 FLC RETURN LAND WHEN THEIR AIRSPD INDICATIONS VARY FROM THE NORMAL. FLT WAS OVERWT DURING LNDG AT DFW; TX.

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THIS WAS THE FIRST FLT FOR THE SHIP'S RETURN TO SVC IS RPTEDLY THE ACFT HAD BEEN PARKED AT DFW FOR 7 DAYS. CAPT CONDUCTED THE WALKAROUND AND NOTICED NO ABNORMALITIES. THE CAPT WAS MAKING THE TKOF. DURING THE TKOF ROLL THE FO MADE HIS REQUIRED XCHK AT 80 KIAS. THE FO NOTICED THAT THE CAPT'S AIRSPD INDICATED 120 KIAS AT THE TIME HIS AIRSPD INDICATED 80 KTS AND BROUGHT THE DISCREPANCY TO MY ATTN. BOTH INDICATORS CONTINUED TO INCREASE; BUT THE FO'S INDICATOR INCREASED SLOWER THAN THE CAPT'S INDICATOR. BASED ON VISUAL CUES AND IRU GND SPD DISPLAY; I CONTINUED THE TKOF AND CLB. DURING THE INITIAL CLB WE GOT A CAUTION AND MESSAGES FOR BOTH THE RUDDER RATIO AND MACH SPD TRIM. THESE CAUTIONS CONTINUED INTERMITTENTLY THROUGHOUT THE FLT. THE ACFT WAS PERFORMING NORMALLY. AT 1000 FT AGL WE SET CLB PWR; FLAPS 5 DEGS; AND 200 KTS IN THE SPD WINDOW. WE TOOK SOME TIME TO ASSESS OUR SIT. ALL 3 AIRSPD INDICATORS WERE SIGNIFICANTLY DIFFERENT AND THE CAUTIONS CONTINUED TO DISTRACT US. I DECIDED TO RETURN TO DFW BUT DID NOT DECLARE AN EMER. PASSING 3000 FT; WE ADVISED ATC THAT WE HAD AIRSPD INDICATION PROBS AND THAT WE WOULD LIKE TO LEVEL OFF AT 5000 FT AND WOULD BE RETURNING FOR LNDG. ATC GAVE US A VECTOR FOR L DOWNWIND FOR RWY 17C AND CLRNC TO 5000 FT. I CONTINUED TO HAND FLY THE ACFT AND COMMUNICATE WITH ATC WHILE THE FO COMPLETED THE AFTER TKOF AND UNRELIABLE AIRSPD INDICATION CHKLISTS. THE CAPT'S; FO'S; AND STANDBY AIRSPD INDICATORS ALL HAD AT LEAST 20 KT VARIANCES BTWN THEM. THE CLOSEST INDICATION TO IRU GND SPD WAS THE CAPT'S INDICATOR; BUT WE WERE STILL UNSURE BECAUSE STANDBY INDICATOR WAS 20 KTS LESS. AS DIRECTED BY THE UNRELIABLE AIRSPD CHKLIST WE DECIDED TO MONITOR IRU GND SPD AND APPLY RPTED WIND TO DETERMINE OUR SPD DURING THE APCH AND BRIEFED FOR A VISUAL ILS RWY 17C APCH. THE DSCNT AND APCH CHKLISTS WERE COMPLETED. A PA WAS MADE ADVISING THE FLT ATTENDANT AND PAX WE WERE RETURNING FOR LNDG. THE HEAD FLT ATTENDANT CAME TO THE COCKPIT AND WAS BRIEFED THAT WE WOULD BE LNDG SHORTLY. ATC CLRED US TO 4000 FT AND GAVE US A BASE LEG TURN FOR A 10 MI FINAL. WE ADVISED ATC THE RWY WAS IN SIGHT AND WERE CLRED FOR A VISUAL APCH. WE CONFIGURED FOR LNDG EARLY. AT 6 MI WE WERE CONFIGURED FOR A FLAPS 30 DEG LNDG; AUTOBRAKES SET TO 2 DEGS; ON LOC AND GS. VREF +30 WAS 134 KTS. RPTED WIND WAS 150 DEGS AT 11 KTS. THE APCH WAS HAND FLOWN; AUTOTHROTTLES OFF. WE MAINTAINED A XCHK BTWN IRU GND SPD; CAPT'S IAS; PITCH AND PWR SETTING. WE WERE ABLE TO MAINTAIN IRU GND SPD OF 130 KTS ON GS WITH VERY LITTLE VARIANCE. THE LNDG WAS IN THE TOUCHDOWN ZONE; LESS THAN 100 FPM DSCNT RATE; TOUCHDOWN GND SPD WAS 125 KTS. MAX REVERSE WAS USED. AUTOBRAKES WERE RELEASED AT 80 KTS. WHILE WAITING ABOUT 5 MINS TO CROSS RWY 17R DFW RAMP WAS NOTIFIED THAT WE WERE RETURNING AND REQUESTED MAINT. AT THAT TIME I NOTICED THAT WE HAD BEEN 5000 LBS OVER MAX LNDG WT FOR LNDG. NEITHER OF US CAUGHT THAT FACT INFLT. WE THEN DISCUSSED BRAKE COOLING FACTORS. AFTER REVIEWING THE LNDG AND ROLLOUT IT WAS AGREED THAT BRAKING WAS MINIMAL. BRAKE TEMP INDICATORS WERE MONITORED DURING TAXI TO THE RAMP AND AFTER ARR AT THE GATE. NONE EVER REACHED AN INDICATION GREATER THAN 2. AT THE GATE; MAINT CAME ABOARD AND WE GAVE THE MECHS THE DETAILS OF OUR PROB. LOGBOOK ENTRIES WERE MADE FOR THE AIRSPD INDICATOR PROB AND OVERWT LNDG. MAINT WAS ABLE TO DUPLICATE THE PROB AT THE GATE USING THEIR TEST EQUIP. EVENTUALLY THE PROB WAS FOUND TO BE PARTIAL BLOCKAGE OF BOTH THE FO AND STANDBY PITOT TUBES. THE TUBES WERE PARTIALLY BLOCKED BY MUD FROM WASPS BUILDING NESTS. NO BLOCKAGE WAS EVIDENT BY EXTERNAL INSPECTION OF THE PITOT TUBES. THE TUBES AND LINES WERE CLEANED OUT BY MAINT AND WE WERE DISPATCHED AND HAD A NORMAL FLT TO ATL. DURING THE WAIT; I HAD A DISCUSSION WITH A LIEN MECH AND ASKED IF PITOT AND STATIC PORTS ARE KEPT COVERED WHEN THE ACFT ARE PARKED FOR EXTENDED PERIODS. THE ANSWER I GOT WAS THAT HE WAS NOT SURE THAT COVERS ARE NORMALLY INSTALLED. MISTAKES MADE: 1) NOT RECOGNIZING WE WERE OVER MAX LNDG GROSS WT. NEITHER I NOR THE FO RECOGNIZED THAT WE WERE OVERWT FOR LNDG UNTIL AFTER THE LNDG WAS COMPLETED. WE WERE APPROX 5000 LBS OVERWT. WHEN I CHKED THE FMS FOR APCH SPD I GOT 134 KTS. BOTH THE FO AND MYSELF WERE NEW TO THE ACFT. I HAD 92 HRS AND THE FO HAD 107 HRS STARTING THE TRIP. (WE DID KNOW EACH OTHER SINCE WE WERE IN TRAINING AT THE SAME TIME BUT HAD NOT FLOWN TOGETHER BEFORE.) A VREF SPD OF 134 KTS DID NOT STRIKE EITHER OF US AS UNUSUALLY HIGH. IN REVIEWING THE OVERWT LNDG PROC IN THE POM THE APCH AND LNDG WAS ACTUALLY CONDUCTED IN ACCORDANCE WITH THE POM WITH THE EXCEPTION THAT WE DID NOT REQUEST TO HAVE GND EMER EQUIP STANDING BY NOR DID I DECLARE AN EMER. THE CHKLIST LISTS THESE AS 'CONSIDERATIONS' BUT NOT REQUIREMENTS. 2) NOT DECLARING AN EMER FOR LNDG. IN HINDSIGHT; I SHOULD HAVE DECLARED AN EMER REGARDLESS OF OUR GROSS WT AS A PRECAUTION IN THE EVENT THERE WAS A PROB AFTER LNDG. HERE ARE SOME OF THE FACTORS I THINK CONTRIBUTED TO THE DECISION TO NOT DECLARE AN EMER -- NOT EXCUSES; BUT I HAVE CRITIQUED MYSELF TO DEATH ON THIS BECAUSE THIS WAS A BAD DECISION THAT COULD HAVE LED TO BIG PROBS IF THE LNDG HAD NOT GONE WELL. A) DURING THE FLT I WAS COMFORTABLE WITH THE ACFT PERFORMANCE DESPITE THE AIRSPD INDICATION PROBS. ONCE WE HAD A GOOD IDEA OF HOW TO MEASURE OUR SPD THE APCH AND LNDG DID NOT SEEM LARGELY UNUSUAL. B) ATC WAS VERY ACCOMMODATING IN CLRING US BACK FOR LNDG AS THERE WAS MINIMAL TFC AT THE TIME. GAINING EXPEDITED HANDLING WAS NOT A PRIORITY BECAUSE APCH WAS VECTORING US FOR A VISUAL APCH BY THE TIME WE FINISHED OUR CHKLISTS. C) THE FO AND I HAVE DISCUSSED THE FLT AND BOTH AGREE THAT DURING THE FLT WE DID NOT FEEL RUSHED OR THAT THE PROB WAS OUT OF HAND. WE HAD ENOUGH TIME TO FIGURE OUT THE BEST WAY TO ASSESS OUR ACTUAL AIRSPD AND PLAN FOR THE APCH. WE DID NOT FEEL AS THOUGH WE HAD TO LAND IMMEDIATELY; BUT AFTER DETERMINING OUR SIT AND OUR NEXT COURSE OF ACTION AN IMMEDIATE LNDG WAS AVAILABLE TO US BECAUSE OF ATC'S HANDLING OF OUR REQUEST. D) NOT RECOGNIZING THE OVERWT CONDITION. IF I HAD RECOGNIZED THE OVERWT CONDITION I AM SURE I WOULD HAVE THEN DECLARED THE EMER; ESPECIALLY IN LIGHT OF THE LIST OF CONSIDERATIONS IN THE OVERWT LNDG PROC IN THE MANEUVERS SECTION OF THE OPERATING MANUAL. OTHER NOTES: WE HAD A B727 CAPT ON THE JUMP SEAT AND HE WAS ABLE TO HELP MONITOR THE VARIOUS AIRSPD INDICATIONS. IN MY DEP BRIEFINGS I ALWAYS BRIEF WX CONDITIONS WITH REGARD TO RETURNING AFTER TKOF. I WILL NOW INCLUDE OUR GROSS WT CONDITION IN THE BRIEFING ALSO. IT HAS TO BECOME A PRIORITY TO PROPERLY PROTECT THE ACFT WHEN IT IS PARKED FOR EXTENDED PERIODS OF TIME. THIS INCIDENT PROBABLY WOULD HAVE BEEN PREVENTED WITH THE USE OF COVERS FOR PITOT TUBES AND STATIC PORTS.