Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Communication Breakdown
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Human Factors; Procedure
Departed [Runway] 26R ONT on the RAJEE3. Controller was extremely busy. Leveled at 7;000 [feet]. Approaching ELLBO wondering if we were going to get 8;000 [feet] or the restriction. Made several radio calls but were ignored. Finally got cleared to 8;000 [feet]. I don't remember the exact distance past ELLBO; but we were left at 8;000 [feet] until what appeared to be within 30 to 40 KM of significantly rising terrain based on GPWS display. The Controller kept telling everyone to not call. We finally tried to call a few times to no avail. I was seriously considering my options if I couldn't get a hold of the Controller regarding terrain clearance. We finally got a hurried call to expedite to 13;000 [feet] call; which we did. I don't want to make a huge deal about this but it felt like we were on the edge of things getting very interesting regarding terrain clearance. Controller busy with planes on approaches and putting off other traffic. I certainly don't know but I might have heard a voice change so possibly training in progress. I know it gets hectic but ATC should at least acknowledge you're there when leaving you low or at an abnormal altitude.
Airline captain reported congested ATC frequency and resulting difficulty obtaining climb clearance to avoid rising terrain on departure procedure.