Date: 201310
Local time of day: 1201-1800
Location: ZDC.ARTCC, VA
Aircraft: Global Express (BD700)
Operator: Fractional
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZDC
ATC / advisory: Center ZDC
Second aircraft: B737-800
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Developmental
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew; Person Air Traffic Control
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: A Global Express checked on at FL410. At Sector 9 we have to descend to hand him off to Sector 35 and I saw his traffic at FL380 southbound so I issued a descent to FL390. First transmission; no reply. Again I issued a descent to FL390. After few seconds passed; the Express said he missed it and on the third time I issued descent to what I could have sworn was FL390. Upon reviewing tapes I issued FL190 and I missed his read back. Listen carefully for every read back especially when the aircraft missed the first clearance. Issue merging target procedures to aircraft in transition.


Second narrative: We were maintaining FL410 controlled by Washington Center northbound in the vicinity of DIW Dixon NDB. The Center Controller assigned us a new altitude as follows. '[Global Express] descend and maintain flight level one niner zero.' I read back; 'Flight level one niner zero [Global Express].' The Flying Pilot set the altitude knob to FL190 and said; 'Flight level one niner zero set.' I replied; 'Flight level one niner zero seen.' The Flying Pilot set vertical speed mode to a descent value. The TCAS display showed traffic at twelve o'clock. Prior to the descent initiation; no traffic had been visible on TCAS. The Pilot Flying said; 'It's kind of an early descent.' I replied; 'I guess they must be busy in the Northeast and Philly is South of New York.' The TCAS traffic turned amber in color and TCAS announced; 'Traffic. Traffic.' At the same time the Controller said; '[Global Express] verify flight level three niner zero.' I transmitted instantly; 'Negative negative altitude assigned flight level one niner zero one niner zero.' After a second's pause; the Controller replied; '[Global Express] turn right immediately.' At this point our altitude was perhaps FL375 or so. The Flying Pilot shallowed the descent rate to nearly zero. An opposite direction airliner with a contrail passed off our eleven or ten o'clock by some number of miles distance. We heard an airliner male voice transmit; 'Center we did not have a resolution advisory. We did not have an RA.' I asked the Controller to please confirm our altitude assignment. I had to ask him twice. He replied; 'Maintain flight level three five zero'; we did so. The remainder of the flight occurred without incident. I promptly advised my Chief Pilot of this event. He telephoned Washington Center hours after the event. An FAA Supervisory Controller indicated there was no violation apparent. Suggestions; hard to say. If you query a controller when you get an early descent; a crew might avoid this error. However; one might also annoy the controller and jam the frequency.


Synopsis: ZDC Controller described a conflict event when issuing a descent to FL190 thinking the altitude assignment issued was FL390; the reporter acknowledging s/he missed the read back by the pilot.