Falcon 2000 flight crew reported descending below the approach clearance due to chart confusion.

Attributes
ACN	1528863
Time
Date	201803
Local Time Of Day	1801-2400
Place
Locale Reference	JFK.Airport
State Reference	NY
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Make Model Name	Falcon 2000
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 20 Flight Crew Total 11000 Flight Crew Type 500
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 20 Flight Crew Total 9000 Flight Crew Type 120
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

While being vectored to runway 04L at jfk; we inadvertently deviated from our final approach altitude to a lower altitude (-400'). Though our current vector was taking us thru the final approach localizer; and maintaining 3;000 feet MSL; we were then given a final heading; speed; altitude and a time to contact tower control (at krstl) instructions. Though we safely managed to identify prior to passing thru the localizer; the final controller then gave us a further right turn to 020 degrees (and controller also mentioned that we could adjust our heading according to reestablish on our own) to intercept the final. Shortly after that new heading; we established ourselves on the final approach course and the pilot flying requested 2;000 feet be set in the altitude select window. While running thru the approach checklists and preparing for landing; I instinctively reached up and set 2;000 feet in the altitude selector and said '2000 set-one to go'. While I returned to the checklist; the pilot flying started a gradual descent. It is then we were told by the final approach controller to maintain 3;000 feet (we were at 2;600 feet). The pilot flying adjusted the aircraft path and leveled back off at 3;000 feet without incident.I acknowledged to the controller that we had traffic ahead in sight and to the right; but he said that it was the traffic behind us that he needed to reference our altitude at 3;000 feet. This incident has been reported to our chief pilot and will be discussed at our next safety meeting to see where we could have done better as a crew. Trust but verify...anytime an altitude or heading may not seem right.

Original NASA ASRS Text

Title: Falcon 2000 flight crew reported descending below the approach clearance due to chart confusion.

Narrative: While being vectored to Runway 04L at JFK; we inadvertently deviated from our final approach altitude to a lower altitude (-400'). Though our current vector was taking us thru the final approach localizer; and maintaining 3;000 feet MSL; we were then given a final heading; speed; altitude and a time to contact tower control (at KRSTL) instructions. Though we safely managed to identify prior to passing thru the localizer; the final controller then gave us a further right turn to 020 degrees (and controller also mentioned that we could adjust our heading according to reestablish on our own) to intercept the final. Shortly after that new heading; we established ourselves on the final approach course and the pilot flying requested 2;000 feet be set in the altitude select window. While running thru the approach checklists and preparing for landing; I instinctively reached up and set 2;000 feet in the altitude selector and said '2000 set-one to go'. While I returned to the checklist; the pilot flying started a gradual descent. It is then we were told by the final approach controller to maintain 3;000 feet (we were at 2;600 feet). The pilot flying adjusted the aircraft path and leveled back off at 3;000 feet without incident.I acknowledged to the controller that we had traffic ahead in sight and to the right; but he said that it was the traffic behind us that he needed to reference our altitude at 3;000 feet. This incident has been reported to our Chief Pilot and will be discussed at our next Safety meeting to see where we could have done better as a crew. Trust but Verify...anytime an altitude or heading may not seem right.

Data retrieved from NASA's ASRS site 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.