A DA50EX experienced fluctuating airspeed and altitude indications after takeoff. The crew could not determine the cause; therefore an emergency was declared as they diverted to a nearby VMC airport.
Synopsis
A DA50EX experienced fluctuating airspeed and altitude indications after takeoff. The crew could not determine the cause; therefore an emergency was declared as they diverted to a nearby VMC airport.
Narrative
[I] took off with ceiling less than 1;000 FT. After gear retraction; at about 400 FT; EGPWS windshear warning activated; airspeed rolled back from 140 KTS; 130 KTS; 120 KTS; 115 KTS. The altimeter showed a climb; copilot and standby instruments followed pilot side. At 4;000 FT altimeter jumped 400 FT to 4;400. We declared an emergency. [I] asked for a vector to return to land. [I was] told to descend to 2;000 FT. On the way down EGPWS went off TOO LOW; we were indicating 4;000 FT on the altimeters. We asked for a clearance to VFR on top. We reached 6;000 FT then requested 8;000 FT and a destination VFR in the area. Enroute checklists were run. No miscompare warnings indicated; but pilot's altimeter would jump 500 FT then go back down. ADC's were checked; AHRS checked; static selectors checked normal then; then back; no change. Ground speed versus IAS with wind looked like IAS was indicating 30 KTS too fast. The divert airport was VFR and landing uneventful. Aircraft has just come out of avionics shop to replace stall vains and had static check done with no problems.
NASA callback
The Reporter stated that Maintenance did not find the problem but he did however have the aircraft's air data computer changed. The Reporter strongly suspects that a static port somewhere was blocked. The aircraft was test flown in various weather conditions and the problem could not be identified. Maintenance believed the cause was ice but the OAT at the time was +15C. In hind sight it appears that the First Officer's instruments were correct but because of the instrument disparity during the initial approach the Captain responded to the worst case instruments and elected a missed approach for troubleshooting. When talking with other DA50 operators since this event he said that there have been similar events in the past.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.