We were at 24,000 feet, unpressurized and on oxygen, as we crossed the Peruvian Andes eastbound toward the Amazon basin. I had selected Talara, Peru, to spend the night before the crossing. In the morning I refueled, checked the weather and notices-to-airmen, and filed our flight plan to Iquitos, Peru. Our twin-engine Piper Navajo was running like a Swiss watch, and that was important, for at all points east, beyond the Andes, any aircraft problem would mean very long delays.
We departed, climbing to the northeast, and when we passed 12,500 feet, I turned on the no smoking sign and told the others to go on oxygen. We continued climbing to 24,000, the safe altitude for crossing over the Chiclayo pass, and then descended into the Amazonas to follow the Marañón River to our destination—Iquitos, Peru.