Global Express (BD700)
Air Traffic Control Developmental
Situational Awareness; Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance
Human Factors
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.
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.
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.