Crosswinds and Mountain Turbulence

On March 3, 2013, in the early afternoon, a Mooney Pilot and three passengers arrived at the Angel Fire, New Mexico, airport (AXX). They had been enjoying the local ski resort and it was time to return to their homes in the San Antonio, Texas area.

The automated weather observation system (AWOS) was reporting winds out of the west from 250 degrees at 33 knots gusting to 47 knots, visibility 10 miles, a clear sky, temperature 47 degrees Fahrenheit, dew point 17 degrees F, and a barometric pressure of 29.93 inches of mercury. The density altitude was calculated at 9,549 feet.  (The north/south runway at Angel Fire is 8,900 feet long, and the airport elevation is 8,379 feet).

Airport manager, Harvey Wright said, “We had all kinds of warnings posted at the front desk, plus we questioned the pilot as to whether he really wanted to go in that weather.”

However, the pilot indicated that he planned to fly and that the winds would not be a problem.

At about 1:20 pm, the pilot taxied his E model Mooney to Runway 17. An FBO employee relayed the current wind and altimeter to the pilot, who repeated the information.

When the Mooney was airborne, it had a significant crab angle into the wind, about 40 degrees right of the runway heading. The airplane rose and fell repeatedly as its wings rocked. Then the airplane’s right wing rose rapidly. The airplane rolled left and descended inverted with the airplane’s nose pointed straight down.”

A witness driving by the airport reported that the Mooney was struggling and only reached an altitude of about 100 feet, hovering momentarily before the left wing dropped and the aircraft descended nose-first to the ground. There were no survivors.

John Verhalen had 459 hours total flight time with 384 hours in type. His occupation was engineering. He had previously worked at Mooney Aircraft Co., and Boeing. At the time of the accident, he was employed by SyberJet.

An old copy of the airplane’s weight and balance found in the wreckage was used to estimate weight and balance. Luggage was destroyed, but the NTSB estimated that it had weighed 60 pounds. With approximately half fuel, takeoff weight was calculated at 2,519 pounds, about 56 pounds below maximum. However, the center of gravity was computed slightly aft of the envelope.

FAA Type Certification Requirements: Maximum Demonstrated Crosswind

Every airplane type certificated by the FAA must first be flight tested to meet hundreds of airworthiness requirements. One of those requirements is a demonstration of crosswind controllability, and more specifically, how the aerodynamics of the airplane allow pilots “with no exceptional skill or alertness” to safely take off and land in crosswind conditions.

The test pilot must be able to control the airplane in 90-degree crosswinds not less than a velocity equal to 0.2 Vso, or the stalling speed of the aircraft in a landing configuration. That is a wind speed equal to at least 20% of the power-off landing configuration stalling speed.

Manufacturers can and often do, test aircraft at crosswind velocities higher than 0.2 Vso, but that’s the minimum speed. In addition to the 0.2 Vso limitation, “The airplane must be satisfactorily controllable in power-off landings at normal landing speed, without using brakes or engine power to maintain a straight path until the speed has decreased to at least 50 percent of the speed at touchdown.” (FAA).

According to former Mooney engineering test pilot Bob Kromer, regarding crosswind landings, “I think you will find a common consensus of test-pilot opinion that most Mooneys can be operated in 90-degree crosswinds up to 15 knots with an acceptable level of pilot workload. Fifteen- to 20-knot winds can be handled but require a much higher level of pilot proficiency and skill in crosswind landing techniques. Twenty knots or above, you should consider finding another airport to land.” Takeoffs might be slightly more forgiving, but this is a good guideline.

Welcome to the Mountains

Angel Fire Airport is in a basin surrounded by mountainous terrain. According to the NTSB, “Mountains to the west and northwest of the airport have peaks between 10,470 and 13,160 feet.

Accident Weather

A weather study was compiled for the accident site. An upper air sound for 1400 mountain standard time (MST) depicted an unstable vertical environment, which would allow mixing of the wind on the lee side of the terrain. Winds as high as 55 knots could occasionally reach the surface. Satellite imagery at the time of the accident, recorded a large amount of standing lenticular clouds near all the mountainous terrain around the accident site. These clouds indicated the presence of a mountain wave environment. At 3:22 a.m. and 11:34 a.m., the National Weather Service issued wind advisories for the accident area that warned of a west-of-southwest wind between 25 and 35 miles per hour (mph) with gusts to 50 mph.”

A weather model predicted a “turbulent mountain-wave environment, with low-level wind shear, updrafts and downdrafts, downslope winds, and an environment conducive for rotors.”

There was no record of the pilot receiving a weather briefing. Airport manager Wright noted that no other flights had arrived or departed that day.

Departing Angel Fire, you must gain altitude quickly or circle around. The mountains to the south are closer to the airport than those to the north. This might be a challenge for a heavy or overloaded aircraft.

Wind can be merely uncomfortable, or disastrous. High winds in the mountains require an appreciation for the power of updrafts, downdrafts, wave action, shear, and rotors.

Twenty-five-plus knots in the mountains is far nastier than similar winds in the midlands and coastal plains. Flying early or late in the day may be a much better strategy than taking off in the middle of the day.

Many pilots use a wind chart to determine the crosswind component. But what if a chart is not readily available? You can use the degree/percentage rules of thumb:

Yes, the degree/percentage rules of thumb are slightly conservative, but they will give you a good understanding of what the winds are about to do to you and your airplane.

METARs from the day of the accident show that a departure at 7 a.m. would have encountered winds of 120 degrees at 8 knots. At 6 p.m., winds were 200 degrees at 8 knots with a lower temperature, lower density altitude, and a far safer scenario.

What’s Your Strategy?

No matter how experienced you are, remember, you are not paid to be a test pilot!

 If the local pilots and airport staff are questioning your intent to fly and looking at you like your head is mounted backwards, that is a red flag. Listen to the voices of experience. Your family will appreciate your caution and professionalism.

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