Later that same year Philip successfully summitted Mt. Cho Oyu, 8201m in Tibet without using supplementary oxygen. Due to the nature of Cho Oyu's large summit plateau, there were inherent risks climbing without supplementary O2, namely the large amount of time required to be spent in the death zone to reach the true summit. On the morning he set out from Advanced Base Camp for the summit of Cho Oyu, he witnessed first hand what later became known as the Nangpa La shootings.