Night in the mountains: most flight training doesn't prepare us for what can happen when we venture beyond the practice area.
As but one example, it took me a long time after earning my private before becoming comfortable with the quality of my flight planning before I could launch on a crosscountry flight with confidence. That confidence had less to do with whether I'd reach my destination than it did whether I had the tools and knowledge to deal with problems cropping up along the way. Relatively fresh pilots with whom I've met recently remind me of those days, so it's easy for me to conclude things haven't changed much.
One example: So little of our flight training is spent climbing to cruising altitude and establishing an efficient cruise configuration. It took me forever to figure out that 2200 rpm in a Skyhawk at 1500 feet MSL was a lot different in power output and speed than the same 2200 rpm at 9500 feet. The former is a great way to putt around and train; the latter is a waste of time if you're trying to go somewhere and paying hourly rental fees.
Another example is brought to the fore this month: How to predict and handle in-flight turbulence. Except for an elementary understanding of a [V.sub.G] diagram, there's very little in current curricula to help new pilots understand and predict where there will be major turbulence. Even relatively experienced pilots--at least by dint of certificates--haven't picked up this knowledge nor have they learned what to do if they encounter it. Exhibit A of our evidence is offered herewith.
On March 7, 2007, at about 2135 Mountain time, a Piper PA-28-235 Cherokee broke apart in flight near Tooele, Utah. The 39-year-old CFI and two passengers were killed; the airplane was destroyed. Visual conditions prevailed for the cross-country personal flight. Four months before the crash, the CFI-pilot reported 430 hours total time.
A witness in another airplane conversed with the accident pilot by radio and was four to five miles in trail. He observed the strobe lights of the accident airplane in front of him. He climbed to 9500 feet but encountered what he described as cumulonimbus clouds and light icing. He descended to 7500 feet where he was below the accident airplane and encountered turbulence severe enough to hit his head violently against the cabin ceiling. He then lost sight of the accident airplane and, although he radioed the other pilot for a weather check, there was no reply. The wreckage was found about 0700 the next day at an elevation of 4310 feet MSL. The debris path covered about .6 of a mile on a heading of 157 degrees.
Recorded ATC radar data depicted the accident aircraft climbing on an easterly course until 2133:47 when it began a left turn to the north for 30 seconds. The next data point was to the right, toward the east, and this was the last "hit" with a beacon code. It occurred at 2134:37 at an altitude of 8200 feet MSL. The last position--of a primary target--was recorded at 2134:47, to the south.
On-site investigation of the wreckage revealed both wings had separated at the root area. The lower left wing separated at the outboard attachment boltholes in a jagged pattern; the spar bent upward. The upper left wing exhibited about 30 degrees of permanent deformation in an upward direction at the separation point. The lower right wing exhibited a similar failure. The aileron cables separated at the wing root in a broomstraw pattern.
The vertical stabilizer separated from the fuselage; the top section of the rudder remained attached to the upper hinge. Most of the rudder remained attached to the empennage at the lower hinge. The rudder surface bent to the right side with extensive wrinkling and buckling.
The left horizontal stabilator separated outboard of the hinge fitting. The surface exhibited a permanent downward deformation with diagonal creases pointing towards the leading edge of the tip section. The right horizontal stabilator separated outboard of the hinge fitting. The surface exhibited a permanent downward deformation.
The engine was substantially impact-damaged but there was no preexisting mechanical defect found.
The closest official weather observation was taken 50 nm east of the accident site at 4227 feet MSL. About 41 minutes before the accident, observed weather included winds from 140 degrees at seven knots, visibility 10 miles and broken clouds at 11,000 feet. Despite the witness-pilot's report of cumulonimbus clouds in the area, there was no mention of a thunderstorm.
The National Transportation Safety Board determined the probable cause of this accident as: "The pilot exceeded the design stress limits of the airplane, which resulted in the in-flight separation of the wings and horizontal stabilizers. Contributing to the accident were the night lighting conditions, clouds, turbulence and icing conditions."
Lacking any apparent record of a nearby thunderstorm or conditions conducive to topography-induced turbulence, the NTSB was left with little choice but to suggest the pilot exceeded the airplane's stress limits. What's more likely is the flight encountered an area of turbulence--probably the result of localized orographic lifting. But--and especially since Cherokees are tough little airplanes--why the pilot either lost control or the turbulence broke the airplane before he could react are mysteries. Usually, turbulence severe enough to break an airplane telegraphs its presence in advance, signalling us to slow down before its full effects can be felt.
It was well after sundown when the accident occurred. While it's unlikely a CFI would inadvertently find himself in IMC and not be able to recover, it's entirely possible he could have blundered into a storm cell generating severe turbulence. Things can happen very quickly in such an encounter, but he did have time to begin a left turn (which may have been a fatal mistake). Instead of turning, an immediate and abrupt power reduction designed to slow the airplane well below [V.sub.A] coupled with an effort to level the wings, might have been the better response. Regardless, it's a shame the accident pilot's training failed to prepare him for this relatively common encounter.
RELATED ARTICLE: Mountain Turbulence
In our opinion, too little attention is paid by most pilot-training texts to the issues of how to predict in-flight turbulence and how to handle it. The FAA's Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25A, has little more than this to say: "The intensity of the turbulence associated with ground obstructions depends on the size of the obstacle and the primary velocity of the wind ... [and] is even more noticeable when flying in mountainous regions. While the wind flows smoothly up the windward side of the mountain and the upward currents help to carry an aircraft over the peak of the mountain, the wind on the leeward side does not act in a similar manner. As the air flows down the leeward side of the mountain, the air follows the contour of the terrain and is increasingly turbulent. This tends to push an aircraft into the side of a mountain. The stronger the wind, the greater the downward pressure and turbulence become. Due to the effect terrain has on the wind in valleys or canyons, downdrafts can be severe. Before conducting a flight in or near mountainous terrain, it is helpful for a pilot unfamiliar with a mountainous area to get a checkout with a mountain-qualified flight instructor."
AIRCRAFT PROFILE: PIPER CHEROKEE 235
ENGINE: LYCOMING O-540-B4B5
EMPTY WEIGHT: 1435 lbs.
MAX GROSS WEIGHT: 2900 lbs.
TYPICAL CRUISE SPEED: 136 knots
STANDARD FUEL CAPACITY: 50 gal.
SERVICE CEILING: 14,500 ft.
RANGE: 2075 nm
Vso: 52 knots
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|Title Annotation:||ACCIDENT PROBE|
|Author:||Burnside, Joseph E. (Jeb)|
|Date:||Mar 1, 2009|
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