Date: 201901
Local time of day: 1201-1800
Location: TNCM.Airport, FO
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch; Taxi
ATC / advisory: Tower TNCM
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Confusion; Situational Awareness
Anomaly: ATC Issue All Types; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Procedure; Human Factors
Primary problem: Procedure

Narrative: We started our day with the flight plan locked out by dispatch. Our dispatcher wanted to know if we were willing to accept a 9 knot tailwind on takeoff so we could use Runway 28 (which heads out to sea) instead of Runway 10 (which points at a low mountain range). Due to climb gradients; we couldn't use Flaps 25 on Runway 10; and that meant we couldn't accommodate all passengers. The Captain and I considered all factors and agreed that we could safely accept a 9 knot tailwind but nothing more. Even though there are ATIS and clearance delivery frequencies published at TNCM; they were not being used. The tower controller was doing it all; he was clearance delivery; he gave push and start clearance in the ramp area; he gave weather reports; he was ground control and tower. He was very busy and his tone of voice on the radio hinted at being overworked. When we contacted him for our clearance; he said it was 'on request.' I also advised him we would need Runway 28 for operational necessity. I felt I'd taken a stressful day and made it worse. He said it might be a long delay because he was working a lot of aircraft inbound to Runway 10. He gave me the latest weather; which included a report of wind '090 at 10 knots.' This was above our 9 knot limit we had talked about. We were already doing a Flaps 25 takeoff with a 27k bump just to do 9 knots of tailwind. 10 knots wasn't going to work for us. The Captain called our dispatcher to advise him of this. He was having connection issues on his cell phone and kept having to walk outside to discuss the performance situation with our dispatcher. It was not an optimal communications situation. We eventually got [new performance data] for a Flaps 5; 27k bump takeoff on Runway 10. But we were going to have to bump 5 passengers to get down to our MTOW. Since the passengers were already on board; this presented a new problem. How do you entice folks who've already checked out of their hotel and are headed home to spend another night in TNCM? The gate agents got on board and started their 'auction' of incentives to get volunteers to stay behind. The process lasted nearly an hour; for reasons I can't fathom. Throughout this process; we had a virtual parade of ground personnel and flight attendants through our flight deck; advising us of what was happening and keeping us apprised of the worsening mood in the back. We finally got the flight close out and called the (overworked) tower controller to get clearance to push. At that time; I advised him we could accept Runway 10. In an almost condescending tone; he said 'Well; that is the runway we're using.' It's a small thing; but in retrospect it kinda set a tone; he wasn't going to entertain any unnecessary radio communications.At TNCM; it's common to get the clearance on taxi out. So this overworked tower controller read; in a rapid-fire fashion; our clearance. What we later found the clearance was is the following: 'PJM B520 STT LAMER; as filed. Maintain Flight Level 150.'It was so rapid fire I didn't write it down fast enough. However; I was looking at the flight plan and thought I heard what I expected to hear. So I read back; directly off the flight plan; this clearance: 'Direct PJM; L451; LAMER; as filed; maintain Flight Level 150.' The controller stated 'Readback correct.' He then gave us taxi instructions. Not quite believing the controller's assurance that my readback was correct; during taxi out; I tried at least 4 times to query the controller to verify our route. My transmissions were continuously blocked due to frequency saturation. I finally got through to the controller and asked him if he had a departure procedure for us to fly or if he just planned to give us vectors. He said he'd give vectors. We were cleared to 'line up and wait on Runway 10 behind Aircraft Y on final.' The [aircraft] in question was at least 3 miles out. I've NEVER been told to line up and wait behind traffic that's 3 milesfrom landing. We complied; but it was another factor that got us out of our comfort zone. On departure; we were given multiple vectors; then cleared 'Direct JUICE.' JUICE was not on our flight plan. The Captain quickly typed it in; then asked the controller to verify our route after JUICE. What followed was a bizarre series of questions that seemed to be the departure controller's attempt to fix blame. He'd say things like 'Didn't you get a proper clearance before takeoff? How is it you know the correct altitude to go to; but you don't have the correct route? How come you know how to go to JUICE but not the rest of your route? I'm looking at your clearance strip and you are NOT supposed to go to SLUGO after JUICE.' Stuff like that. Meanwhile; we were about 30 seconds from crossing JUICE and I had no idea which way to turn after that. With confusion still reigning supreme; the departure controller handed us off to San Juan. After the Captain quickly explained our situation to San Juan; we thankfully got a course to fly after JUICE. It is our belief that we were on our assigned route the entire time and did not deviate from what we were instructed to do. We just needed clarification of our route after JUICE. However; it could have gone very badly. Factors included complicated performance planning on a very performance-limited runway. Stressors included having to bump passengers; a very busy tower controller who was close to being overwhelmed; and an inaccurate hearback/readback; with the controller hearing what he expected to hear just as I did. I know it's common in the Caribbean to get clearances on taxi-out; but it's not an optimal situation; especially with changes to our routing. It effectively takes the captain out of the loop as he/she is taxiing. After we discovered our mistake; we needed clarification in a timely manner. We didn't need to get an interrogation from the departure controller trying to figure out who to blame. In the end; we trapped our error and fixed it before deviating from our clearance. But it was close. Way too close.




Synopsis: Air Carrier First Officer reported pre-departure ATC communication difficulties almost led to a track deviation departing TNCM.