AOPA Pilot Magazine - August 2023 - 16

LETTERS
the absence of aeromedically significant cognitive
or psychological deficits. There are times,
fewer to be sure, when I advocate for safety by
documenting significant deficits. CogScreen
is one tool that, in my opinion, is essential in
allowing me to do a better job in advocating for
safety, and therefore for pilots.
Carlos R. Porges
Key Biscayne, Florida
Mechanic crisis
After reading Mike Busch's opinion on the paucity
of mechanics in the May issue, I can only
agree with much angst. My pilot friends tell me
of the long wait to get even the most basic work
performed, never mind annual inspections. But
those in the experimental arena who are lucky
enough to build their own aircraft can apply for
a repairman's certificate. In these trying times
maybe there should be a pathway for a pilot/
owner who is willing, competent, and capable
to earn a similar repairman's certificate for
their own airplane. Those who have performed
owner-assisted annual inspections on the same
airplane over a number of years are likely to have
the incentive, experience, and capability of doing
a more than adequate job of ensuring the airworthiness
of their craft. They could be an expert in
that one particular airplane. Perhaps it is time
for the FAA to consider a restricted airframe and
powerplant license just as we have progressive
levels of pilot certification from student to ATP.
Ramon Pabalan
Fort Myers, Florida
Reality check
One thing I've learned reading AOPA Pilot over
the years is that Catherine Cavagnaro knows a
lot more about flying than I do. The 70-50 rule,
which recommends aborting takeoffs at 50 percent
of the runway length if you haven't reached
70 percent of your rotation speed, has been one of
the notes in my collection of useful aviation information.
Yet Cavagnaro says it doesn't work.
So, I set up a spreadsheet based on the performance
of my airplane, calculating position
and speed as a function of time during a sea level
takeoff roll. She's right! The 70-50 rule assumes a
constant acceleration rate...and barely works in
that case. When I adjust the acceleration for drag,
using my maximum sea-level cruise to define the
speed where thrust equals drag, and assume drag
increases as a square of speed, then the 70-50
rule leaves me 3 percent short of rotation speed
at the end of the runway.
16
AOPA PILOT / August 2023
Around the office we refer to
AOPA Director of Photography
Chris Rose as " MacGyver. " If you
remember the 1985 television
series, you know that the title
character could problem solve
any situation ( " If I had some duct
tape, I could fix that " is one of his
famous lines). Well, Rose employs
duct tape and more when he
encounters a challenging photo
assignment; he is especially
fond of zip ties. To capture the
joy Senior Photographer David
Tulis felt after flying his Tri-Pacer
across the country ( " Happy to
Be Here, " p. 50), Rose wanted Tulis relaxing with his new bird. But to
get above and look down at the chill pilot, Rose needed to get creative.
No drones allowed at the airport, so two bulb-replacement extenders,
some zip ties, and a clamp or two later, Rose had a contraption he and our
new intern Charlie Beadle could hover over with the camera mounted
to the top and a remote switch to shoot the photo. Beadle said he never
expected his internship to be this much fun.
A rule of thumb that barely gets you off the
end of the runway seems absurd anyway. As she
suggests, it would be better to use the takeoff
roll calculation in your POH and add a generous
margin. Alternately, a conservative rule of
thumb (at least for my airplane which can decelerate
on the ground faster than it can accelerate)
would be " off the ground at mid-field or abort. "
Mike Koerner
Palos Verdes, California
Your June article completely misses and misconstrues
the point of a basic math equation
which says that even at constant acceleration
during a takeoff roll, you will have used every
inch of runway before hitting VR
reached 70 percent of VR
if you have only
at midfield. And with
less than constant acceleration-as your author
argues for at length-you have even less than
this 0 percent safety margin, making this an
extremely viable No-Go reference point.
Henry Fiorentini
Lincolnshire, Illinois
Catherine Cavagnaro responds: AOPA received
many letters in defense of the rule that many pilots
use that, if you don't have at least 70 percent of the
rotation speed by the 50 percent mark, abort. Of
course, what that means is if these pilots do have
70 percent of the rotation speed halfway down
the runway, they will probably
continue the takeoff. It's a dangerous
rule for many reasons
as there is no guarantee that
the pilot will have 100 percent
of rotation speed at the end of
the runway. And even if it does
happen to work out, planning
on lifting off near the end of the
runway is just a nonstarter.
Since the 70 percent is
derived from a model that
ignores air resistance-a factor
that is more critical during the
second half of the takeoff roll-
I maintain a 100 percent rule
based on rotation point is safer.
There is nothing like knowing
your airplane so you can pad
the predicted number appropriately
and ensure the runway
still provides that distance plus
that necessary to bring the airplane
to a stop.
Send letters to pilot@aopa.
org or Editor, AOPA Pilot,
421 Aviation Way, Frederick,
Maryland 21701. Letters may
be edited for length and style.
AOPA Pilot Magazine - August 2023

Table of Contents for the Digital Edition of AOPA Pilot Magazine - August 2023
