AN ACR MLG HAD A NAV ERROR AND DSNDED IN RESPONSE TO A TCASII COMMAND.

Narrative

AS THE CAPT SLOWED HIS RATE OF CLB PASSING FL270 TO LEVEL OFF AT FL280; ZDC CALLED TO ASK IF WE WERE ON AN ASSIGNED HDG. THIS CONFUSED US AS WE THOUGHT WE WERE HDG OUTBOUND FROM SBY ON J79. AS WE WERE CHKING OUR COURSE AND REALIZED THE CAPT WAS FLYING OUTBOUND ON THE 205 DEG RADIAL VICE 225 DEG RADIAL; CTR GAVE US DIRECT TO KINSTON (ISO). DURING THIS CONFUSION; THE CAPT ROTATED THE AUTOPLT THUMB WHEEL TO LEVEL OFF AT FL280. AT THIS TIME; BOTH OF US HAD OUR HEADS IN THE CHARTS; LOOKING UP ISO. THE NEXT THING WE KNEW; THE ALT ALERT WENT OFF. THIS SURPRISED US BOTH AS WE WERE SURE WE HAD LEVELED OFF. THE AUTOPLT WAS JUST BARELY OUT OF THE LEVEL POS AND HAD A SLIGHT CLB GOING. THE CAPT IMMEDIATELY DISENGAGED AUTOPLT AND BEGAN A MANUAL DSCNT. JUST AS THE CAPT DISENGAGED THE AUTOPLT; WE RECEIVED AN RA ON OUR TCASII. THIS WAS THE FIRST AND ONLY WARNING WE RECEIVED ON TCASII. NO TA. WE HAD ALREADY BEGUN THE DSCNT BACK TO FL280 AND WE HAD VISUAL ACQUISITION OF THE TFC; SO WE MADE NO EVASIVE MANEUVER. WE ALSO HAD A LITTLE OVER 100 FT DIFFERENCE IN THE 2 ALTIMETERS; SO THE FO SHOWED MAX ALT AT 28400 FT WHILE THE CAPT INDICATED JUST UNDER 28300 FT. THE OTHER TFC RPTED AN RA ALSO. WHEN CTR ASKED US TO CHK OUR ALT; WE WERE ALREADY BACK LEVEL AT FL280; AND SO STATED. THIS INCIDENT WAS INITIALLY CAUSED BY POOR COCKPIT LIGHTING RESULTING IN READING THE WRONG RADIAL. THE COPLT SHOULD ALWAYS VERIFY THAT THE PF HAS THE APPROPRIATE NAVAIDS SET CORRECTLY. THIS WAS A CASE OF POOR CREW COORD. SUPPLEMENTAL INFORMATION FROM ACN 249894: ORIGINAL NAV MISTAKE WAS CAUSED BY MISREADING MY OWN HANDWRITING ON THE CHART HOLDER NOTE PAD IN A DARK COCKPIT. I SHOULD HAVE MONITORED THE LEVEL OFF AT FL280 UNTIL COMPLETED RATHER THAN PLACING SO MUCH TRUST IN THE AUTOPLT.