Narrative:

We were flying at FL290 at an airspeed of 260 kts. When ATC gave us a clearance of 'maintain 290 until salyy and then descend via the anjll 4 arival at 260 kts.' I was the pilot monitoring and took this to mean fly 290 kts. Until salyy and then descend via the arrival at 260kts. The controller meant this as maintain FL290 until salyy; and then descend via the arrival at 260 kts. The next altitude on the arrival was glesn between FL300 and FL240 so when we began our descent before salyy the controller very quickly told us we were entering a restricted area and to climb to FL290. After receiving the clearance the pilot flying expressed some confusion with the clearance and I repeated back the clearance to him; and told him the controller wanted 290 kts. Until salyy. He asked me to clarify the clearance with the controller. I asked how else could that be interpreted; and he said he heard the 290. So I thought; ok you heard 290; and I heard 290 where is the confusion? It wasn't until he began to descend from FL290 that I first thought uh oh! That's what he was confused about and a few moments later ATC came on and told us to climb back up to FL290. The immediate cause of this event was the controller and I both reading the clearance without the words maintain flight level 290; and instead just maintain 290; which lead to confusion of whether he wanted 290 kts. Or FL290. But; also; this was very poor CRM on my part in not clarifying the clearance with ATC. In my mind; the clearance was clear; and I showed stubbornness in not wanting to clarify a clearance with ATC. And that was; perhaps; compounded with the flying pilot not stating clearly what he was confused about. Regardless of that though; when asked to clarify the clearance; I should not have hesitated to do so.

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Original NASA ASRS Text

Title: CRJ-700 Captain reported misinterpretation of ATC clearance of altitude and speed resulted in altitude deviation and airspace violation.

Narrative: We were flying at FL290 at an airspeed of 260 kts. when ATC gave us a clearance of 'maintain 290 until SALYY and then descend via the ANJLL 4 arival at 260 kts.' I was the Pilot Monitoring and took this to mean fly 290 kts. until SALYY and then descend via the arrival at 260kts. The Controller meant this as maintain FL290 until SALYY; and then descend via the arrival at 260 kts. The next altitude on the arrival was GLESN between FL300 and FL240 so when we began our descent before SALYY the Controller very quickly told us we were entering a restricted area and to climb to FL290. After receiving the clearance the pilot flying expressed some confusion with the clearance and I repeated back the clearance to him; and told him the Controller wanted 290 kts. until SALYY. He asked me to clarify the clearance with the Controller. I asked how else could that be interpreted; and he said he heard the 290. So I thought; ok you heard 290; and I heard 290 where is the confusion? It wasn't until he began to descend from FL290 that I first thought uh oh! That's what he was confused about and a few moments later ATC came on and told us to climb back up to FL290. The immediate cause of this event was the Controller and I both reading the clearance without the words maintain Flight Level 290; and instead just maintain 290; which lead to confusion of whether he wanted 290 kts. or FL290. But; also; this was very poor CRM on my part in not clarifying the clearance with ATC. In my mind; the clearance was clear; and I showed stubbornness in not wanting to clarify a clearance with ATC. And that was; perhaps; compounded with the flying pilot not stating clearly what he was confused about. Regardless of that though; when asked to clarify the clearance; I should not have hesitated to do so.

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.