Gulfstream G280
Flight Crew Flight Engineer; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 72; Flight Crew Total 10521; Flight Crew Type 1082
Communication Breakdown
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Aircraft; Human Factors; Procedure
We were descending in ZZZ. ATC asked our speed; and I replied '320 knots; but we can give you more.' The controller asked for 'best forward speed;' and I replied that we would comply. We were later assigned a descent to cross ZZZZZ Intersection at 12;000. We responded and began the descent at the appropriate time. In the G280; VMO decreases from about 340 down to 300 KIAS as you descend from the low 20's to 10;000. We maintained best forward speed throughout our descent; but the controller asked if we were still doing 320 as we neared ZZZZZ Intersection. I responded that we had slowed; but we're still giving him best forward speed. He told us to let him know before we slow. I believe that he vectored an aircraft off the arrival; behind us; but do not believe any separation was lost. In this case; I didn't connect his desire for us to maintain 320 knots; with what I understood to be 'best forward speed.' In the future; I will be more careful accepting an ambiguous airspeed clearance; knowing that we have so much variation in VMO at lower altitudes.
G280 Captain reported an issue with ATC in regards to understanding best forward speed.