AOPA Pilot Magazine - February 2018 - 88

P&E

TECHNIQUE

'Round the patch
A potential solution to reduce pattern risk
B Y L E W I S A R C H E R A N D D AV I D J A C K K E N N Y

THE AIRPORT TRAFFIC PATTERN is established as a staple of general aviation
flight activity during presolo training,
and remains so for many pilots throughout their careers. Whether it's polishing
up crosswind landings, fine-tuning the
power-off one-eighty in preparation for a
fixed-wing commercial checkride, or just
logging a little time when conditions aren't
conducive to leaving the airport, nearly
everyone who's flown powered, heavierthan-air aircraft is familiar with taking a
quick buzz around the patch.
Each circuit is traditionally divided into
five legs-departure/upwind, crosswind,
downwind, base, and final-separated by
90-degree turns. The origin of this technique is obscure, but it's gone virtually
unchallenged for years. Still, the airman
certification standards don't define what
the traffic pattern should look like, nor
does any other FAA publication or regulation explicitly state that it must be a
rectangle. (Occasional calls from tower

88 | AOPA PILOT February 2018

controllers to "square your base" also
imply some pilot discretion.) A brief scan
of the accident data suggests that we may
just be doing this wrong.
The AOPA Air Safety Institute's analysis of accidents involving unintended stalls
found that half took place in the traffic pattern, and more than two-thirds of those
during the turns to base or final were fatal.

The origin of the
traditional traffic
pattern is obscure,
but it's gone virtually
unchallenged for years.
Except for the experience of the
pilots involved-an 82-year-old, 18,000hour commercial pilot and a 62-year-old,
8,000-hour CFI-the May 3, 2012, crash
of a Beechcraft Bonanza was fairly typical. A witness saw a steep bank during

the base-to-final turn develop into an
uncontrolled descent that took the lives
of these two highly experienced aviators. The NTSB found the probable cause
to be "the pilot's excessive bank angle...
which resulted in an inadvertent aerodynamic stall and spin" and noted that wind
conditions were "conducive to a runway
overshoot," providing support to the belief
that the pilot had made an aggressive effort
to realign the aircraft with the runway after
overshooting the base-to-final turn.
For its part, the NTSB has identified
preventing "loss of control in flight" (a
frustratingly broad description) in general
aviation as one of its "most wanted" safety
improvements for the past three years.
In the 2016 version of this list, the NTSB
identified "losses of control"-i.e., stalls-
during approach to landing, maneuvering,
and initial climb as the deadliest because
of the limited time and altitude available
for recovery. Possible remedies include
greater emphasis of angle-of-attack awareness during training and flight reviews and
the addition of AOA indicators to cockpit
instrumentation, but one of the simplest
and most effective could be a slight modification to the traffic pattern itself.
An attractive alternative to the traditional rectangular pattern is the so-called
"rounded-base turn" pattern, which
replaces the squared base leg with a
constant, gentle turn from the end of
downwind onto final. This is similar to the
technique often used by pilots conducting
"power-off 180" maneuvers during a simulated (or real) engine failure in the traffic
pattern-as well as to the overhead pattern entries taught to military pilots for
decades. The potential benefits include
lower and more stable bank angles and
reduced likelihood of being misaligned
with the runway upon completion of the
turn, decreasing the risk of the kind of
overshoot accident described earlier.
The first steps toward assessing those
benefits were taken at the University of
North Dakota in the winter of 2016-2017.
Flight instructors in the aerospace program
flying Garmin G1000-equipped Cessna
172S Skyhawks found that the roundedbase turn pattern did not differ greatly
AOPA Pilot Magazine - February 2018

Table of Contents for the Digital Edition of AOPA Pilot Magazine - February 2018
