FLYING Magazine Technicalities

Peruvian Excursion Provides a Lesson in High Vapor Pressure

What is going to the airplane engine is more like froth than fuel.

Peter Garrison

Monday, August 19, 2024 at 09:02 AM ET

Verified

Edited By: tccjeremy

Salina de Maras, the traditional Inca salt field in Maras near Cuzco in Sacred Valley, Peru. [Adobe Stock]

Key Takeaways:

A pilot experienced recurring fuel pressure fluctuations and engine unsteadiness at high altitudes during a flight from Lima over the Andes and Amazon, initially misdiagnosing the problem.
Despite attempts to resolve the issue by turning back and checking fuel filters, the problem persisted, leading to a challenging flight through remote and unfamiliar airspace.
Upon arrival in Bogotá, the pilot learned from a local expert that the fuel had high vapor pressure, a common issue in the region that required keeping the boost pump on at altitude.

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Lima, Peru, is overcast, as usual. We try to cancel IFR and turn on course once we’re on top, but the controllers insist on keeping us with them until Salinas, 40 miles down the coast. We finally cross Salinas at 12,000 feet and swing around northeastward. The Andes are close, rearing out of the stratus deck into a cloudless sky.

At 15,000 feet I notice that the fuel pressure is fluctuating. I watch the gauge intently. The tempo of the engine is unsteady. The fluctuations become larger and longer.

Peter Garrison

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, ""Technicalities"" and ""Aftermath,"" with FLYING readers.