Complex sentence: Two airline captains had their licences revoked and an assistant captain was suspended, after it was found that the co-pilot was seated in the cabin while the assistant captain was in the cockpit, the high altitude airport requires two experienced captains to be at the controls.
Split into simpler sentences: Two airline captains had their licences revoked and an assistant captain was suspended, after it was found that the co-pilot was seated in the cabin while the assistant captain was in the cockpit. The high altitude airport requires two experienced captains to be at the controls.