Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Took Evasive Action
Aircraft; Weather
During cruise flight at our planned cruising altitude of FL370; we encountered mountain wave and up/downdrafts. During the hour or so in cruise at FL370 leading up to the event; we were constantly changing the power; attempting to maintain our filed cruise speed of M.77. At one point; the airspeed started to drop towards M.74. I selected the climb detent. Instead of increasing; the airspeed started decreasing. At about M.72 I selected MAX POWER (APR thrust). I told my First Officer (FO) to ask ATC for a lower altitude. ATC said it would be 3 minutes before they could grant a descent clearance. The airspeed continued to decrease; even though we were still set at APR thrust. Once the speed decreased to approximately M.705 and showed a negative trend vector; I started approximately 1;000FPM descent and instructed my FO to inform [Center] that we were in a descent. Within about 600 feet descent; we were able to regain our normal airspeed and returned to a normal flight profile at FL350 with an amended ATC clearance. Flying at a lower altitude than our planned cruising altitude during times of strong jetstream winds and mountain wave would give us a greater margin to recover airspeed lost due to a downdraft.
[Report narrative contained no additional information.]
CRJ-900 flight crew reported descended from assigned altitude of FL370 when they were unable to maintain speed because of downdrafts.