Outside The Envelope

Check the POH before takeoff when unfavorable conditions like tailwinds and high altitude combine.


When was the last time you cracked open your aircraft’s flight manual or pilot’s operating handbook? You know, the thick book in which you’ll find information on the aircraft’s limitations, equipment, normal and emergency procedures and performance charts? If you’re like most non-commercial pilots flying the same aircraft day in and day out, it’s probably been a while.

That’s not necessarily a bad thing. When you first start flying a certain type, spending a quiet evening with its manuals is a good decision. Even through the first several hours, referring to the book is common. But after a few years and several hundred hours, pilots tend to know—without looking at the book—what the aircraft will do under certain conditions. If and when there’s a question—say, the emergency gear-extension procedure, or to ensure the loading is correct—the book is right there to answer the questions. But we don’t need the book to determine if, say, a Cessna 150 can get off a level, 5000-foot-long runway at sea level on a standard day at gross weight and in calm winds. That question was settled long ago and—unless someone chains some anvils to it—it’ll be fine. Somewhere between that C150 on a mile-long runway and the landing-gear extension procedure is a gray area, one possibly leading us to doing something for which the aircraft isn’t approved.

Knowing when to pull out the book can be as much an existential “thing” as a scientific one. The basic rule of thumb we’d suggest is to pull out the book whenever there’s a question, or when conditions are outside your experience with the aircraft. Aside from a smart-aleck passenger asking if you know how to fly the aircraft, there’s no downside (and the smart-aleck can stay on the ground).

The book should be used to confirm and verify what you already know, or to answer questions about something you’ve never encountered before. Knowing when to pull it out and read it should never be embarrassing and always identify the pilot as conscientious, safety-minded. Here’s a great example why.

On June 11, 2010, at about 1354 Mountain time, a Piper PA-32R-300 Lance sustained substantial damage when it impacted a building near Eagar, Ariz., during takeoff initial climb from the Springerville (Ariz.) Municipal Airport (D68). Visual conditions prevailed. The private pilot and three passengers were killed. There were no reported ground injuries. The flight was originating at the time of the accident.

A witness watched the airplane take off from Runway 11; it “used more runway than used by most of the other small aircraft during takeoff.” The witness stated that after takeoff, the airplane was “rocking side to side” and appeared to be “having trouble gaining altitude.” The witness further reported that the airplane “gained altitude” then “lost altitude” three or four times. Another witness observed the airplane “turn its wings at an angle when it crashed into the roof.”

The airplane impacted a high school building about 0.96 statute miles east of the departure end of Runway 11. The wreckage debris path was about 230 feet in length and oriented on an approximate heading of 050 degrees magnetic. The measured elevation for the accident site was about 7045 feet msl; the published field elevation at D68 is 7055 feet msl.

The recovered engine, airframe and flight control system components revealed no evidence of pre-impact mechanical malfunction. Review of sales receipts from the departure airport’s self-service fuel pump revealed the accident airplane received 76.41 gallons of 100LL prior to departure. Fuel samples were free of contaminants, including water.

At 1350, four minutes before the accident, the automated weather observation system (AWOS) at D68 reported wind from 210 degrees at 25 knots, gusting to 32 knots, temperature of 25 degrees C, and an altimeter setting of 29.99 in. Hg. Density altitude was reported to be 9700 feet. At 1355, one minute after the accident, winds were from 170 degrees at 24 knots, gusting to 31 knots.

Based on the 1350 weather observation, the flight’s crosswind component for Runway 11 ranged from 25 to 32 knots, with a tailwind component from four to five knots. The 1355 observation at D68 translates into a crosswind component of 21 to 27 knots, and a headwind of 12 to 16 knots.

Using the reported basic empty weight of the airplane provided by Piper Aircraft, reported weight of the occupants, 98 gallons of fuel and 100 pounds of luggage, the airplane was found to be within weight and balance and center of gravity limitations. The aircraft’s demonstrated crosswind component was established by the manufacturer at 17 knots. Its pilot’s operating handbook, POH, notes in its performance section “…information derived by extrapolation beyond the limits on the charts should not be used for flight planning purposes.”

The POH’s takeoff performance charts revealed the weather conditions present at the time of the accident exceeded the chart’s performance parameters for both flaps-up and flaps-partially extended configurations. As a result, takeoff performance calculations were not determined. Using the manufacturer’s performance calculation charts, reported weather conditions and maximum gross weight of the airplane, gear-down climb performance was calculated to be about 90 fpm; the gear-up climb performance was calculated to be about 410 fpm.

Probable Cause
The National Transportation Safety Board determines the probable cause of this accident to include: “The pilot’s operation of the aircraft outside of the manufacturer’s specified performance limitations, which resulted in the pilot’s failure to maintain clearance from buildings and terrain during takeoff initial climb.”

Recalling that the maximum demonstrated crosswind component is not an operational limitation, the pilot’s real takeoff performance issues were the gusty tailwind and high density altitude. The airplane got airborne but its climb performance indicates the landing gear wasn’t retracted, producing a marginal climb rate. The NTSB report is silent on the landing gear’s position.

We’ll never know if the pilot knew his takeoff attempt was outside the airplane’s published flight envelope, but the combination of a gusty tailwind and high density altitude should have set off alarm bells. The same is true for anyone confronted with conditions possibly outside the envelope.




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