A WDB ACR LOST PART OF ONE OF ITS REVERSERS.

Narrative

ON DSCNT INTO THE JFK AREA AT APPROX FL240; I NOTICED THE REVERSE ISOLATION LIGHT AND REVERSE INTRANSIT LIGHT ON THE L ENG CAME ON MOMENTARILY. SOON AFTER WE HEARD A LOUD NOISE AND FELT A SHARP JOLT. A VISUAL INSPECTION FROM A CABIN WINDOW REVEALED A PARTIAL COWLING LOSS ON THE L ENG; BUT NO FURTHER DAMAGE COULD BE SEEN FROM THE GND. WE MADE A NORMAL VISUAL LNDG AT JFK ALL ACFT SYSTEMS WORKED NORMALLY. I DO NOT KNOW WHAT CAUSED THE COWLING TO DEPART THE ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. THE REVERSER HAD BEEN LOCKED OUT PER THE ACR MEL PRIOR TO LEAVING EUROPE BECAUSE MAINT HAD FOUND A CRACK IN THE TRACK THAT OPERATES THE REVERSER. THE PART THAT LEFT THE ACFT IS FIBERGLASS. ALL REVERSERS ARE BEING MODIFIED AND THE MEL IS BEING CHANGED BECAUSE OF THIS INCIDENT. THERE WAS VERY SLIGHT DAMAGE TO THE UNDERSIDE OF THE WING AND THE ENG NACELLE. SUPPLEMENTAL INFO FROM ACN 229360. A FLYBY OF THE ARPT WAS MADE SO TWR AND MAINT PERSONNEL COULD LOOK AT THE PLANE. THEIR RPT CONFIRMED WHAT HE SAW. GEAR AND FLAPS WERE EXTENDED BY NORMAL SYS AND A NORMAL LNDG WAS MADE. THE EQUIP WAS ON THE SCENE AND COM BTWN FIRE DEPT AND MECHS AND ATC VERY GOOD.