Date: 201412
Local time of day: 1201-1800
Location: TNCM.Airport, FO
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: Center TJZS
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure; Airport; Airspace Structure
Primary problem: Ambiguous

Narrative: Inbound to TNCM; crossed SLUGO intersection at FL120 (transition level FL065) encountered extreme frequency congestion on Juliana Approach; instructed to slow to 210 KIAS.  Requested descent and instructed to maintain FL120 and enter holding at GABUL intersection with no other information provided.  Extreme volume of radio traffic prevented further instruction.  Turned direct GABUL and entered standard holding inbound to GABUL on the 347 degree bearing to (IF/IAF) AVAKI depicted on the RNAV (GNSS) RW 10 approach; 12-1.  Corporate jet entering SLUGO instructed to maintain FL130 indicating 800 feet above us passed opposite direction within 2 NM inside at the apex of our north holding turn; no TCAS alert.  Suspect they'd transitioned their altimeters (local 30.03) at FL180 instead of the prescribed FL065.  They entered holding above us; so we maintained position 180 degrees out/opposite in our hold.  Another aircraft entered from SLUGO at FL120 on course direct SXM and I could see on TCAS that he was proceeding inside of our depicted holding pattern at our altitude at our 4 o'clock position as we proceeded on a 167 degree track to GABUL.  Juliana Approach issued instruction for that aircraft to 'turn immediately to 110 degrees.'  I could see that our right turn outbound from GABUL would place us in direct conflict with that aircraft's path; so instructed FO PF to make a left turn at GABUL and transmitted forcefully that we were turning left in holding to avoid traffic conflict at our altitude.  Controller responded with vector east and descent clearance.  Subsequent vectors to approach and an otherwise uneventful landing. Traffic and frequency congestion today was absolutely epic.  Traffic poured in from SLUGO and was instructed to hold at GABUL; which places these aircraft's holding track in direct conflict with last received routing clearance from San Juan of SLUGO direct Juliana.  Suggest an arrival plan be devised which allows holding be assigned at an intermediate fix that eliminates conflicting tracks with aircraft arriving over SLUGO; and that this plan be depicted for aircrew.  Further; that complete holding instructions be transmitted by Juliana Approach.




Synopsis: B737 Captain experiences traffic and frequency congestion of absolutely epic proportions upon entering TNCM airspace. Holding instructions are not complete and at least one aircraft is holding with the wrong altimeter setting. The reporter uses his own initiative to avoid an aircraft passing through the holding pattern at the same altitude; before ATC takes notice and issues vectors to separate the aircraft. Reporter suggests better planning and more holding fixes further from the airport are in order.