Narrative:

While on an instrument flight plan, during descent to roa, we were given clearance to descend from cruising altitude of 13000 ft MSL to 6000 ft MSL. During the period of level flight at 6000 ft MSL, ATC called that he got an altitude warning showing us to be at 3700 ft MSL. Some high terrain is located near this airport, as high as 4000 ft. He expressed concern at our apparent altitude. I assured ATC that we were level at 6000 ft MSL. Shortly thereafter he asked for my name and home base. Since we were on final for runway 33 and doing checklists I asked for a number to call him after landing. During the phone conversation, he said that a record is kept (in roa area) of such events. I gave him the requested information and said we would use another transponder on departure. I asked and he confirmed that there was no indicated conflict with other aircraft, only that high terrain points are close to the airport. During the phone conversation, the controller asked if this happened before. I said it happened once. (It was my thought that the first error in altitude the previous week was due to excessive radar interrogations while flying near active military exercises. Our transponder reply light was on almost continuously.)

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Original NASA ASRS Text

Title: THE RPTR IS OBSERVED BY APCH CTL RADAR TO BE AT 3700 FT WHILE VISUAL AND ALTIMETER INDICATIONS WERE AGREEING AT 6000 FT.

Narrative: WHILE ON AN INST FLT PLAN, DURING DSCNT TO ROA, WE WERE GIVEN CLRNC TO DSND FROM CRUISING ALT OF 13000 FT MSL TO 6000 FT MSL. DURING THE PERIOD OF LEVEL FLT AT 6000 FT MSL, ATC CALLED THAT HE GOT AN ALT WARNING SHOWING US TO BE AT 3700 FT MSL. SOME HIGH TERRAIN IS LOCATED NEAR THIS ARPT, AS HIGH AS 4000 FT. HE EXPRESSED CONCERN AT OUR APPARENT ALT. I ASSURED ATC THAT WE WERE LEVEL AT 6000 FT MSL. SHORTLY THEREAFTER HE ASKED FOR MY NAME AND HOME BASE. SINCE WE WERE ON FINAL FOR RWY 33 AND DOING CHKLISTS I ASKED FOR A NUMBER TO CALL HIM AFTER LNDG. DURING THE PHONE CONVERSATION, HE SAID THAT A RECORD IS KEPT (IN ROA AREA) OF SUCH EVENTS. I GAVE HIM THE REQUESTED INFO AND SAID WE WOULD USE ANOTHER XPONDER ON DEP. I ASKED AND HE CONFIRMED THAT THERE WAS NO INDICATED CONFLICT WITH OTHER ACFT, ONLY THAT HIGH TERRAIN POINTS ARE CLOSE TO THE ARPT. DURING THE PHONE CONVERSATION, THE CTLR ASKED IF THIS HAPPENED BEFORE. I SAID IT HAPPENED ONCE. (IT WAS MY THOUGHT THAT THE FIRST ERROR IN ALT THE PREVIOUS WK WAS DUE TO EXCESSIVE RADAR INTERROGATIONS WHILE FLYING NEAR ACTIVE MIL EXERCISES. OUR XPONDER REPLY LIGHT WAS ON ALMOST CONTINUOUSLY.)

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