Narrative:

I was the international relief officer on [this flight]. Arriving into kiah; the controller cleared our flight to descend via the MSCOT2 RNAV arrival. He subsequently assigned us to fly at 300 KIAS which is 20 knots above the published speed of 280 KIAS on the STAR. The crew flew the arrival in the LNAV/VNAV mode. The controller asked the crew to keep our speed up as long as possible. At mscot the aircraft leveled off at 10;000 feet and began slowing to 250 KIAS. The controller immediately queried the crew as to why we were slowing. He stated that he intended for us to keep up our speed till domno due to following traffic. He immediately issued south turn to following traffic. The flying pilot then disconnected the autopilot and continued to descend though 10;000 feet increasing our speed. We were flying 290 down to 8000 feet when we began to slow to 250. There was a lack of communication between ATC and the crew. The ATC controller assumed we would continue to domno before we descended through 10;000 feet and slowed. The crew left the aircraft in VNAV and allowed it to begin slowing at mscot. The clearance from ATC to keep our speed up was not definitive. The confusion led to our exceeding 250 knots below 10;000 MSL.

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Original NASA ASRS Text

Title: A VHF debate erupted between Approach Control and the flight crew of a B-777 when the controller's request to keep their speed up on the MSCOT RNAV STAR to IAH conflicted with the flight crew's desire to be below 10;000 feet and; thus; at 250 KTS as they approached DOMNO; which is required to be crossed between 10;000 feet and 8;000 feet.

Narrative: I was the IRO on [this flight]. Arriving into KIAH; the controller cleared our flight to descend via the MSCOT2 RNAV arrival. He subsequently assigned us to fly at 300 KIAS which is 20 knots above the published speed of 280 KIAS on the STAR. The crew flew the arrival in the LNAV/VNAV mode. The controller asked the crew to keep our speed up as long as possible. At MSCOT the aircraft leveled off at 10;000 feet and began slowing to 250 KIAS. The controller immediately queried the crew as to why we were slowing. He stated that he intended for us to keep up our speed till DOMNO due to following traffic. He immediately issued S turn to following traffic. The flying pilot then disconnected the autopilot and continued to descend though 10;000 feet increasing our speed. We were flying 290 down to 8000 feet when we began to slow to 250. There was a lack of communication between ATC and the crew. The ATC controller assumed we would continue to DOMNO before we descended through 10;000 feet and slowed. The crew left the aircraft in VNAV and allowed it to begin slowing at MSCOT. The clearance from ATC to keep our speed up was not definitive. The confusion led to our exceeding 250 knots below 10;000 MSL.

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.