During a cross-country flight under instrument flight rules (IFR), the Piper PA-32R-300 pilot was cleared from 9,000 feet to 7,000 feet over mountainous terrain.
In the descent, he reported encountering instrument meteorological conditions (IMC) and extreme turbulence, which caused a loss of control, resulting in inverted flight.
He was able to recover from the loss of control, but was unable to recall how he recovered.
After the upset and recovery, he landed without further incident near Gatlinburg, Tennessee.
According to information obtained from a Safety Board meteorology specialist, weather data displayed a band of clouds in the immediate vicinity of the upset location associated with mountain wave activity and locally generated turbulence.
Another aircraft in the immediate vicinity also reported an encounter of moderate-to-severe turbulence prior to the event.
There were no AIRMETs or SIGMETs in effect in the area where the turbulence was encountered.
During a post-flight inspection, both wings were substantially damaged after wrinkling and tearing was found.
Probable cause: The pilot’s encounter with extreme turbulence during descent over mountainous terrain, which resulted in a loss of control, and structural damage in flight.
NTSB Identification: GAA15CA051
This April 2015 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Mountain waves can cause changes in altitude well up into the flight levels but seldom cause significant turbulence however a rotor wave can be generated on the leeward side of mountains at the lower altitudes when strong surface winds exist and that will definitely play havoc with a light airplane including flipping it inverted and overstressing the airframe as happened in this story. A big clue for the presence of a rotor wave would be the appearance of the characteristic lenticular or lens shaped clouds.
Mountain wave is an analog wave of wind with peaks and valleys and high to extreme air movement. You can be pushed high or pushed down beyond your power and control. Lenticular clouds form at the tops of the wave characteristically equally spaced apart across a valley leeward from the mountain range.
Rotor is just like is sounds. It’s a high speed rotating wind that will disrupt flight like clear air turbulence but do it in a continuous way.
Updraft winds create lenticulars over the top of a mountain range. Those are not rotors per se.
Flipped inverted, with turbulence severe enough to cause structural damage to the wings. Not only is the plane toast but his underwear are shot as well…says I
Not only that, but to have landed uneventfully. Wow. The rest of his days are borrowed time. He should wake up every morning, kiss the ground he’s walking on, and thank sweet Jesus he’s still here…says I ?
Mountain flying is no joke. Mountain wave should not have flipped him over, but a rotor winds would do it especially if you fly parallel on the leeward side of a mountain in such a wind.
The docket contains scant information. The pilot said he was initially at 10,000 feet 20 miles from his destination. He descended to 9,000 feet and was cleared to 7,000. During the descent he said he had “a 50 kt headwind… near the Smokey Mountains.” IMHO, 50 kts of headwind should be interpred as a BIG red flag for severe turbulence over mountains. The meteorologists said there was a mountain wave line near the mountains… which this pilot evidently wasn’t aware of. There is no mention in the Docket or factual report whether or how the pilot obtained his preflight weather. He was on an IFR flight plan.
You’re right John, with a 50 it headwind over the Smoky’s the pic should’ve seen the red flag and flown to the alternate airport out of harms way. At least he survived the incident in the school of hard knocks and can fly another day.