Narrative:

The WX I observed on this night was something I have never seen before in my 18 yrs as an air traffic controller. After discussing the sequence of events with the NWS personnel and the pilot of the aircraft, we feel it may be something called a 'gravity wave.' there was a recent occurrence of a gravity wave in vermont in jan/98. Before the NWS told us what this WX anomaly was, no one at btv tower or any of the local pilots had ever heard of such a term. The ramifications of this type of WX activity are very serious and should be studied to see if it could be the cause of certain 'unexplained accidents.' basically, this is what happened: in a 23 min period, we had a 14 point drop in the barometric pressure. The wind remained fairly steady at 10-15 KTS from the sse during the drop in pressure. At the bottom of the pressure drop (29.60) we had a momentary power failure in the tower and TRACON. Btv AFSS lost power for over 2 hours at this time. The wind had sharply increased to 40 KTS from the ese and the pressure climbed very sharply to 29.74 in just 4 mins (14 points). As the barometric pressure rose, the wind switched direction again to a wnw flow at 20-25 KTS. As the pressure stabilized the winds dropped off to less than 10 KTS from the southwest. The aircraft in question (aircraft X) departed runway 15 just as the pressure was rising. There were no signs of any convective activity in the area. I radar idented the aircraft and turned him to a northwesterly heading for plattsburgh, ny, and climbed him to 2600 ft MSL. Moments later, the pilot reported unable to maintain altitude and wanting to return immediately to burlington. I observed him at 4000 ft MSL and I issued him a heading and altitude to get into VMC conditions so he could get a visual approach as he had climbed into IMC conditions. The pilot said he was at idle power and his vsi was fully pegged and he was in an uncontrolled climb. At the same time the aircraft's gear warning alarm was sounding and he was encountering strong turbulence and buffeting. Finally, the pilot was able to begin a descent back to burlington and was able to execute a visual approach when he broke out of the clouds at 2000 ft MSL. By now, the winds had shifted to the northwest and the pilot elected to land runway 33. On his turn to base leg for runway 33, the pilot encountered a severe downdraft situation and had to apply full power to keep the aircraft in the air. He said his vsi was pegged in a maximum descent. This event was very localized as we had a DO328 aircraft depart less than 2 mins after aircraft X with no adverse WX encountered. As I said earlier, there were no thunderstorms in the area and actually the bases of the clouds before this event wre around 7000 ft or 8000 ft. We hope to get the doppler radar tapes from btv NWS in the near future and this may help to explain this unusual event. Maybe ASRS can publish some information to pilots and controllers alike in the future ASRS callback to help educate the aviation community on the effects of a 'gravity wave.'

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Original NASA ASRS Text

Title: A DEPARTING TWIN ENG CARGO PLANE WAS UNABLE TO MAINTAIN ALT AND CONTINUED TO CLB WHILE ENCOUNTERING STRONG TURB IN A RPTED PERIOD OF RAPIDLY RISING PRESSURE. THE ACFT ON RETURN TO THE ARPT SUBSEQUENTLY ENCOUNTERED A SEVERE DOWNDRAFT WHILE IN DSCNT AND AT FULL PWR. RPTR CLAIMS THAT NWS PERSONNEL RPTED THE ANOMALY TO BE A GRAVITY WAVE.

Narrative: THE WX I OBSERVED ON THIS NIGHT WAS SOMETHING I HAVE NEVER SEEN BEFORE IN MY 18 YRS AS AN AIR TFC CTLR. AFTER DISCUSSING THE SEQUENCE OF EVENTS WITH THE NWS PERSONNEL AND THE PLT OF THE ACFT, WE FEEL IT MAY BE SOMETHING CALLED A 'GRAVITY WAVE.' THERE WAS A RECENT OCCURRENCE OF A GRAVITY WAVE IN VERMONT IN JAN/98. BEFORE THE NWS TOLD US WHAT THIS WX ANOMALY WAS, NO ONE AT BTV TWR OR ANY OF THE LCL PLTS HAD EVER HEARD OF SUCH A TERM. THE RAMIFICATIONS OF THIS TYPE OF WX ACTIVITY ARE VERY SERIOUS AND SHOULD BE STUDIED TO SEE IF IT COULD BE THE CAUSE OF CERTAIN 'UNEXPLAINED ACCIDENTS.' BASICALLY, THIS IS WHAT HAPPENED: IN A 23 MIN PERIOD, WE HAD A 14 POINT DROP IN THE BAROMETRIC PRESSURE. THE WIND REMAINED FAIRLY STEADY AT 10-15 KTS FROM THE SSE DURING THE DROP IN PRESSURE. AT THE BOTTOM OF THE PRESSURE DROP (29.60) WE HAD A MOMENTARY PWR FAILURE IN THE TWR AND TRACON. BTV AFSS LOST PWR FOR OVER 2 HRS AT THIS TIME. THE WIND HAD SHARPLY INCREASED TO 40 KTS FROM THE ESE AND THE PRESSURE CLBED VERY SHARPLY TO 29.74 IN JUST 4 MINS (14 POINTS). AS THE BAROMETRIC PRESSURE ROSE, THE WIND SWITCHED DIRECTION AGAIN TO A WNW FLOW AT 20-25 KTS. AS THE PRESSURE STABILIZED THE WINDS DROPPED OFF TO LESS THAN 10 KTS FROM THE SW. THE ACFT IN QUESTION (ACFT X) DEPARTED RWY 15 JUST AS THE PRESSURE WAS RISING. THERE WERE NO SIGNS OF ANY CONVECTIVE ACTIVITY IN THE AREA. I RADAR IDENTED THE ACFT AND TURNED HIM TO A NORTHWESTERLY HDG FOR PLATTSBURGH, NY, AND CLBED HIM TO 2600 FT MSL. MOMENTS LATER, THE PLT RPTED UNABLE TO MAINTAIN ALT AND WANTING TO RETURN IMMEDIATELY TO BURLINGTON. I OBSERVED HIM AT 4000 FT MSL AND I ISSUED HIM A HDG AND ALT TO GET INTO VMC CONDITIONS SO HE COULD GET A VISUAL APCH AS HE HAD CLBED INTO IMC CONDITIONS. THE PLT SAID HE WAS AT IDLE PWR AND HIS VSI WAS FULLY PEGGED AND HE WAS IN AN UNCTLED CLB. AT THE SAME TIME THE ACFT'S GEAR WARNING ALARM WAS SOUNDING AND HE WAS ENCOUNTERING STRONG TURB AND BUFFETING. FINALLY, THE PLT WAS ABLE TO BEGIN A DSCNT BACK TO BURLINGTON AND WAS ABLE TO EXECUTE A VISUAL APCH WHEN HE BROKE OUT OF THE CLOUDS AT 2000 FT MSL. BY NOW, THE WINDS HAD SHIFTED TO THE NW AND THE PLT ELECTED TO LAND RWY 33. ON HIS TURN TO BASE LEG FOR RWY 33, THE PLT ENCOUNTERED A SEVERE DOWNDRAFT SIT AND HAD TO APPLY FULL PWR TO KEEP THE ACFT IN THE AIR. HE SAID HIS VSI WAS PEGGED IN A MAX DSCNT. THIS EVENT WAS VERY LOCALIZED AS WE HAD A DO328 ACFT DEPART LESS THAN 2 MINS AFTER ACFT X WITH NO ADVERSE WX ENCOUNTERED. AS I SAID EARLIER, THERE WERE NO TSTMS IN THE AREA AND ACTUALLY THE BASES OF THE CLOUDS BEFORE THIS EVENT WRE AROUND 7000 FT OR 8000 FT. WE HOPE TO GET THE DOPPLER RADAR TAPES FROM BTV NWS IN THE NEAR FUTURE AND THIS MAY HELP TO EXPLAIN THIS UNUSUAL EVENT. MAYBE ASRS CAN PUBLISH SOME INFO TO PLTS AND CTLRS ALIKE IN THE FUTURE ASRS CALLBACK TO HELP EDUCATE THE AVIATION COMMUNITY ON THE EFFECTS OF A 'GRAVITY WAVE.'

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.