LGA LNDG RWY 22 DEPARTING RWY 31; WIND 270 DEGS 52 KTS. LNDG ACR ON GAR SAME TIME ACR DEPARTING. LOSS OF SEPARATION RESULTING IN SYS ERROR.

Narrative

THE CAPT WAS THE PF. THE WX WAS NIGHT VFR. APCHS WERE BEING FLOWN TO RWY 22 AT LGA; WITH DEPS USING RWY 31. ON BASE LEG; WE WERE GIVEN CLRNC TO FOLLOW THE PRECEDING ACFT FOR APCH TO RWY 22. WE SQUARED THE TURN TO FINAL AND REDUCED TO FINAL APCH SPD TO FOLLOW THE PRECEDING ACFT. ATIS WINDS WERE 270 DEGS AT 18 KTS GUSTING TO 27 KTS. WINDS ON FINAL WERE 270 DEGS AT 52 KTS; SO WE WERE IN A SIGNIFICANT R CRAB AS WE FLEW DOWN FINAL. AS WE GOT CLOSE TO THE RWY; IT BECAME APPARENT THE PRECEDING ACFT WOULD NOT CLR THE RWY IN TIME FOR US TO LAND. AS WE WERE INITIATING A GAR ON OUR OWN; THE LGA TWR CTLR DIRECTED US TO GO AROUND AND FLY RWY HDG. AFTER LOOKING INSIDE THE COCKPIT MOMENTARILY TO RECONFIGURE THE ACFT FOR THE GAR; THE FO AGAIN LOOKED OUTSIDE AND OBSERVED A B737 ON TKOF CLBOUT AT OUR 10-11 O'CLOCK POS FLYING VERY SLIGHTLY ABOVE US FROM L TO R. THE FO STATED TO THE CAPT; 'WATCH OUT FOR THIS GUY;' AND INITIATED EVASIVE ACTION BY PUSHING FORWARD ON THE YOKE. THE CAPT THEN ALSO OBSERVED THE B737 AND CONTINUED EVASIVE ACTION BY REDUCING THE CLB RATE. THE B737 PASSED OVER US WITH VERY LITTLE CLRNC; APPROX 200 FT OR LESS. WE RECEIVED NO TCASII RA/TA ALERTS/ADVISORIES. WE WERE THEN GIVEN VECTORS FOR ANOTHER APCH AND LNDG TO RWY 22 WHICH WAS UNEVENTFUL. AFTER LNDG; THE CAPT CALLED THE TWR SUPVR WHO ADVISED THAT THEY WERE ALREADY INVESTIGATING THE INCIDENT. SUPPLEMENTAL INFO FROM ACN 460116: LGA CONDUCTING LDA A TO RWY 22; THEN SWITCHED TO ILS 22 APPROACH. WX 270/18G27 10SM 230 650 11/08 2947. LLWAS. TKOFS WERE CONDUCTED ON RWY 31. WE WERE CLRED INTO POS AND HOLD RWY 31. ACR Z JET WAS CLRED TO LAND RWY 22. AS HE LANDED; WE WERE CLRED FOR TKOF. AS WE WERE ROTATING OFF RWY 31; ACR X WAS ORDERED TO GO AROUND DUE TO ACR Z NOT CLEARING RWY 22 QUICK ENOUGH. WE HEARD THE CONTROLLER ISSUE GO AROUND AND STARTED LOOKING FOR ACR X. FO ACQUIRED ACFT AND COMMANDED EVASIVE MANEUVER TO AVOID MIDAIR COLLISION. ACR X SLID UNDERNEATH US BY APPROX 200 FT. CTLR NEVER SAID A WORD OR ISSUED ANY EVASIVE ACTION INSTRUCTIONS TO EITHER ACFT. UPON ARRIVAL AT IAD; CALLED THE SUPERVISOR AT LGA TOWER AND HE ACKNOWLEDGED THE INCIDENT. HE CONFIRMED THAT THE TAPES WERE PULLED AND AN INVESTIGATION WAS UNDERWAY.