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Recent NTSB data confirm that botched base to final turns are as common as stall/spin in loss of control.
- Recent NTSB data confirm that botched base to final turns are as common as stall/spin in loss of control.
- If I could, I’d do an NTSB study on base to final loss of control from slipping turns, not just skidding turns. I have demonstrated spins from slipping turn entries in a C152, so they are possible, I just don’t know how common they might be.
- Wind can affect base to final turns .
Confirmation of Previous Results
Back in 2015, the EAA held a contest to reduce loss of control accidents. Being a good systems engineer, I looked at the data from 551 RV-series airplane events over the past 25 years. There wasn’t enough data to be statistically significant, unless you knew more about statistical quality control than I could find on the net, but of 24 base to final accidents:
Seven (7) were clearly botched base to final turns, with the same aerodynamics as a botched steep turn at altitude, i.e., a spiral.
Four (4) were very clearly stall/spin;
Thirteen (13) could not be determined.
As reported in AirFactsJournal.com (What NTSB Reports Say About Impossible Turns and AOA (Part I), September 9, 2024 and Part II, September 13, 2024), this past year I reviewed two years of Part 91, single engine NTSB reports. Although the motivation was to look at the relationships between AOA and impossible turn accidents, the data was already sorted to expose base to final events. Those two years’ data contained the following traffic pattern events:
NTSB # | Mechanism | Comment |
ERA22FA399 | Low Speed Spiral (botched turn) | Base to final, very tight, 100° bank angle, 15° nose down,
2,500 fpm, “indicating that the airplane did not stall before the crash”, low experience pilot |
CEN23FA046 | Low Speed Spiral (botched turn) | Base to final. Recorded data says no spin. |
WPR22FA331 | Low Speed Spiral (botched turn) | Base to final, engine failure |
ERA23LA010 | Low Speed Spiral (botched turn) | Base to final, low AOA, good speed |
WPR22FA215 | Low Speed Spiral, maybe spin | Base to final, very low traffic pattern |
ERA23FA046 | Spin, maybe Low Speed Spiral | Overshot base to final |
ERA22LA394 | Spin (presumed) | Base to final, student pilot |
WPR22FA215 | Spin likely | Base to final, CFI/student, 200′ on downwind |
CEN22LA129 | Spin likely | Turning crosswind |
WPR22FA235 | Spin over runway | Turning final |
ANC22LA038 | Spin* external cause, gusty | Downwind to base, gusty, spin & recovered |
WPR23LA018 | Spin* external cause, wake turbulence | Wake turbulence spin, base to final |
These events are split 50:50 botched turn spiral / spin. Each category has four definites and one probable.
Note that there were two upsets (loss of control not caused by pilot inputs). Gusty conditions might have been mitigated by an airspeed cushion, but if conditions were gusty, an AOA indicator might not have been readable. Even if the AOA was readable in the gusts, it might have been very difficult to fly a flight path with more AOA cushion – more speed seems a more reasonable mitigation.
The takeaway is confirmation of earlier results: in base to final accidents, only about half are stall/spin, and the other half are botched steep turn / spirals.
And just like a VFR into IMC spiral is low AOA, ball centered, a botched base to final turn can be low AOA, ball centered. Here is an example, flown in my RV-9A, eyes out of the cockpit, with no attempt to manage AOA or skid ball.
In other words, an AOA indicator will give an alert in only half of base to final turn accidents.
The data has spoken.
Spins from Slipping Turns
There are many statements that say that a base to final spin cannot happen from a slipping turn. However, I used to demonstrate that slipping base to final spin entry to my primary students right before I sent them for their check ride, just so that they would take the base to final turn with appropriate seriousness.
This kind of spin entry is also known as a “spin over the top,” because when entering the spin from a turn, the airplane will spin towards the higher wing. In other words, in a turn to the left, the right wing will be high, and the spin will be to the right, towards the high wing and over the top.
Determining how many base to final turn accidents were from slips or skids will not be easy. The impact signature may tell which wing hit first, and the location of the wreckage may indicate whether it was a left- or right-hand pattern. NTSB data will sometimes have usable photos in the dockets, but not always.
Some plane will have digital data recording, such as Cirrus and some more recent experimental aircraft. Sideslip angle, i.e., slip or skid, can sometimes be read from lateral acceleration.
Here’s how to demonstrate a spin over the top.
First, make sure that the PIC is qualified, and that there is lots of altitude. Spin training is essential for the PIC, and snap roll training is also helpful.
Perform a 45° banked turn, but do not add back pressure. Rather, when the nose drops, use top (opposite) rudder to hold the nose up. This will give you a cross-controlled configuration, a slip. To keep the turn going, add back pressure. As the plane starts to slow down, add a little bit of power. When the stall warning horn goes off, say the magic incantation, “C’mon, baby, you’ve got this!” and add just a little more back pressure. Then hang on.
In the Cessna 152, this will in effect give a snap roll. A CFI friend relates that when he was taking an advanced maneuvers course in his Cessna 177RG, he observed similarly dramatic results.
There’s a lot more to this topic than I have personally researched, and more work required than I am willing to do on real world prevalence of slip/skid accidents. This is a great topic for somebody else.
I find it credible that most base to final spin accidents are from skidding turns. On the other hand, I very seriously question the assertion that it is not possible to do a spin entry from a slipping turn, because I used to demonstrate those to my primary students.
Too Shallow Turns, Base to Final
A rectangular traffic pattern is a ground reference maneuver. Just like a constant radius turn around a point, a rectangular pattern will require compensation for wind. In the presence of wind, precise rectangular pattern turns may require less or more bank angle, and some turns may be less or more than exactly 90°.
With wind aligned with base leg, for example, a crab angle will be required on final. Thus, the base to final turn will be 90° plus the crab angle. In addition, the higher ground speed on base will require the pilot to start the turn sooner and to bank more sharply to fly a precise ground track, base to final.
I don’t recall reading much if anything about the effects of wind on turns in the traffic pattern and how wind might be a precursor to base to final loss of control. In a strong wind, the results would be noticeable, of course.
Postscript: The traffic pattern turn ideas were inspired by Catherine Cavagnaro’s column, Timid Turns, published in AOPA Pilot, November 2024, on too shallow turns, base to final.
- Final Thoughts on the Base to Final Turn - January 31, 2025
- What NTSB Reports Say About Impossible Turns and AOA (Part II) - September 13, 2024
- What NTSB Reports Say About Impossible Turns and AOA (Part I) - September 9, 2024
In this video, the late Richard McSpadden demonstrates a spin over the top, i.e., a spin entered from a slipping turn. This was shot in an Extra, but a Cessna 152 can also give quite a ride. https://www.youtube.com/watch?v=el6rQw-yTYY&t=564s
If the video doesn’t start at the spin, the time of the spine is 9:24 into the video. Don’t know why the time stamp got lost…
Dr. Wischmeyer, Great topic that’s been around since the beginning. Leighton Collins, editor of the original Air Facts, discusses this in depth in his “The Dangers of the AIr” addendum to Wolfgang Langewiesche’s iconic book Stick and Rudder. His article is a bit long winded but in a nutshell, maneuvering at low altitude and low airspeed (i.e. base to final turns) leaves no room to recover from an upset. Recent video from security cameras and iPhones shows vividly how quickly a ship can depart and literally fall out of the sky. I wrote an article discussing this issue “Loss of Control at Low Altitude-The Base to Final Turn” published in the November 2021 issue of the American Bonanza Society Magazine. One of the main points of the article is the danger of a fairly strong tail wind on base leg leading to an illusion of speed coupled with an overshoot of the runway center line and subsequent steeply banked turn to correct for the overshoot. There are other issues involved and discussed in the article but these are the main points. These videos would be a good training tool to alert us all of the need to prevent loss of control especially at low altitude.
Geary – I agree that tailwind on base is a huge factor in starting a dangerous sequence. But I’m sure you’d agree that the bank isn’t the cause of loss of control because there are plenty of examples of glides to landings, spirals to landings from above the airport, and 180° turnbacks involving steep banks where nothing bad happens. The culprit is losing awareness and control of the pitch position while the steep bank is happening.
I have a Lift Reserve AOA meter in my airplane and train with it regularly. The idea is to get a good feel for the airplane during all ground reference maneuvers. I also limit my bank in the pattern to 45° or less and if I overshoot the base to final turn, I continue the turn and come back to final course at a 30° angle. I take the potential for danger in all ground reference turns seriously. I think these precautions have served me well over the years.
One of the most important things you do is demonstrate hazards that can occur base-to-final, which will automatically include understanding of how one gets into a hazardous condition and then how to recover from it. This is in contrast to the guideline of never exceeding 30° of bank base-to-final. That’s a reasonable guideline except when something totally unexpected happens, you may find yourself in an attitude you’ve never seen before, and near the ground. The wrong involuntary reaction on the controls will probably follow.
Barry Schiff has a good article in AOPA from December 2011 called “the no-spin zone”, describing the spin over the top.
A couple of common elements in these example crashes seems to be poor airmanship and loading up the wing inappropriately. I am curious about the proficiency of the pilots in the examples you studied. This article reminded me of a recent video of influencer Xavi Caballol and partner spinning an airplane in ay low altitude (they survived); this spin seemed to be triggered by a fistful of throttle while low, slow, steeply banked, and at high AOA.
Great question, but inadequate information to study it.