Large Transport
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Total 8000
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented
Environment - Non Weather Related; Human Factors
On approach into Quito; SEQM; we were cleared for the ILS Z 36. The approach requires we maintain FL180 until crossing QIT VOR. The Captain was pilot flying. Upon getting cleared for approach and in VNAV PTH he set minimums in the altitude window. He was a little high to make the altitude crossing and the recommended speed of 220 KIAS at QIT. I was looking up our missed; single engine missed; taxi and gate location on my iPad when I looked over to see the CA (Captain) had selected vertical speed mode; 3000 FPM down and was descending through 17;100 ft prior to QIT; instead of maintaining FL180 for terrain clearance as depicted and briefed on approach. I quickly advised him to level off as we were not yet permitted to descend on approach. Quito Approach queried us and we explained we were maintaining 17;000 feet. The remainder of the approach and landing occurred without incident and NO EGPWS EVENT WAS TRIGGERED.
Air carrier First Officer reported the Captain began a descent too early in a high terrain area.