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.

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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.'