Narrative:

Deviation from ATC clearance under captain's emergency authority/authorized. Aircraft had leveled off at cruise. Non radar departure controller advised us of a VFR airplane 12 O'clock position, 500 ft below, 3 mi. TCASII showed another aircraft (ATR42 or similar) at 12 O'clock position, 3.5 mi in a high rate of descent towards us. Since I could not descend towards the VFR below (this aircraft may have been on a VFR plan, but he was in the clouds) I elected to make a right turn. As soon as we saw the descending IFR level less than 500 ft above us, and pass within .5 mi, we returned to course and advised ATC. This controller was tasked with clearance delivery, ground tower and approach and departure control. He was severely overloaded -- not his fault. Post event: sxm ATC very incensed we had taken evasive action. Captain provided name, and that I turned the aircraft under emergency authority/authorized. Controller overworked beyond his capacity -- non radar environment. With traffic this dense, very dangerous situation. Manning level off, st marten tower totally inadequate. Prior to our departure, this controller had an airbus A340 and a B767 circling at the same altitude in close proximity to each other off the west end of runway 9 at sxm. For this controller, a non radar environment meant constantly making position queries of all aircraft. This caused bad frequency congestion. Callback conversation with reporter revealed the following information: TCASII RA gave a descent command as the lower traffic was not detected by TCASII. The reporter's TCASII showed 2 aircraft, but no altitude on aircraft Y, the VFR traffic. The VFR traffic was IMC in VFR flight, not visible and had no mode C, it not being 'required' in that area. As to flight Z, the controller reasoned that the turn made by the reporter was not required as he expected the ATR Z to level off at the assigned altitude. That ATR flight was crewed by a foreign flight crew with a heavy accent. Reporter stated that a yr ago a company flight had a very close near midair collision during the departure procedure with another aircraft. In a few days the company is holding a meeting with their safety department and the FAA to discuss this ongoing situation. There is no radar, the controller is handling multiple position and the frequency congestion from at least 10 aircraft was insufferable. Controller was 'guessing' as to other aircraft position, having to constantly request position of respective aircraft.

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Original NASA ASRS Text

Title: MULTIPLE POTENTIAL CONFLICTS AND FREQ CONGESTION PLAGUES A B737-800 FLC DURING A NON RADAR DEP PROC FROM TNCN, FO.

Narrative: DEV FROM ATC CLRNC UNDER CAPT'S EMER AUTH. ACFT HAD LEVELED OFF AT CRUISE. NON RADAR DEP CTLR ADVISED US OF A VFR AIRPLANE 12 O'CLOCK POS, 500 FT BELOW, 3 MI. TCASII SHOWED ANOTHER ACFT (ATR42 OR SIMILAR) AT 12 O'CLOCK POS, 3.5 MI IN A HIGH RATE OF DSCNT TOWARDS US. SINCE I COULD NOT DSND TOWARDS THE VFR BELOW (THIS ACFT MAY HAVE BEEN ON A VFR PLAN, BUT HE WAS IN THE CLOUDS) I ELECTED TO MAKE A R TURN. AS SOON AS WE SAW THE DSNDING IFR LEVEL LESS THAN 500 FT ABOVE US, AND PASS WITHIN .5 MI, WE RETURNED TO COURSE AND ADVISED ATC. THIS CTLR WAS TASKED WITH CLRNC DELIVERY, GND TWR AND APCH AND DEP CTL. HE WAS SEVERELY OVERLOADED -- NOT HIS FAULT. POST EVENT: SXM ATC VERY INCENSED WE HAD TAKEN EVASIVE ACTION. CAPT PROVIDED NAME, AND THAT I TURNED THE ACFT UNDER EMER AUTH. CTLR OVERWORKED BEYOND HIS CAPACITY -- NON RADAR ENVIRONMENT. WITH TFC THIS DENSE, VERY DANGEROUS SIT. MANNING LEVEL OFF, ST MARTEN TWR TOTALLY INADEQUATE. PRIOR TO OUR DEP, THIS CTLR HAD AN AIRBUS A340 AND A B767 CIRCLING AT THE SAME ALT IN CLOSE PROX TO EACH OTHER OFF THE W END OF RWY 9 AT SXM. FOR THIS CTLR, A NON RADAR ENVIRONMENT MEANT CONSTANTLY MAKING POS QUERIES OF ALL ACFT. THIS CAUSED BAD FREQ CONGESTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: TCASII RA GAVE A DSCNT COMMAND AS THE LOWER TFC WAS NOT DETECTED BY TCASII. THE RPTR'S TCASII SHOWED 2 ACFT, BUT NO ALT ON ACFT Y, THE VFR TFC. THE VFR TFC WAS IMC IN VFR FLT, NOT VISIBLE AND HAD NO MODE C, IT NOT BEING 'REQUIRED' IN THAT AREA. AS TO FLT Z, THE CTLR REASONED THAT THE TURN MADE BY THE RPTR WAS NOT REQUIRED AS HE EXPECTED THE ATR Z TO LEVEL OFF AT THE ASSIGNED ALT. THAT ATR FLT WAS CREWED BY A FOREIGN FLC WITH A HVY ACCENT. RPTR STATED THAT A YR AGO A COMPANY FLT HAD A VERY CLOSE NMAC DURING THE DEP PROC WITH ANOTHER ACFT. IN A FEW DAYS THE COMPANY IS HOLDING A MEETING WITH THEIR SAFETY DEPT AND THE FAA TO DISCUSS THIS ONGOING SIT. THERE IS NO RADAR, THE CTLR IS HANDLING MULTIPLE POS AND THE FREQ CONGESTION FROM AT LEAST 10 ACFT WAS INSUFFERABLE. CTLR WAS 'GUESSING' AS TO OTHER ACFT POS, HAVING TO CONSTANTLY REQUEST POS OF RESPECTIVE ACFT.

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.