Jet Crew: Reverse Thrusters Failed in Chicago - Washington Post

"Jim Macklin" wrote

If I remember correctly, the 727 had a series of landing
accidents because the full flap setting was about 50-60
degrees and if the pilot got too slow, they could not
recover. Maximum extension was reduced.
Looking on the Internet, I found a further limitation for
couple approaches with certain autopilots. Is there any
early 727 pilot out there with the facts on the first 727
and any changes in certification re flaps?

Go back to your little airplanes Jim. The following article is
from the May-June 1965 issue of the Boeing Airliner. Is that
far enough back for you?

"Flap Angle
One of the factors having the greatest effects
on stall and initial buffet speeds is the angle the
flaps are set at during flight. The 727 flap angles
are given in trailing edge deflections of 0, 2, 5,
15, 25, 30 and 40 degrees. An increase in flap
angle increases the camber of the wing so that
it will produce the same lift at a lower speed than
a smaller flap angle setting would produce. The
effect of flap angle on initial buffet and stall can
be seen in Figures 2, 3, and 4 for flap angles 0,
15, and 40 degrees. The graphs also present the
points where the stick shaker operates and shows
the 7 percent margin required by Civil Air Regulations
for adequate stall warning. In all cases, except at 30
and 40 degree flaps, initial buffet will occur at a
speed higher than the 107 percent stall speed
requirement. However, initial buffet is never less
than 4 percent above stall speed even at 40° flaps.
Since the reference landing speed (Vref) is 130
percent of the stall speed, there is adequate speed
margin for landing."

Besides flying the line in the -200 series from 1986-
1991, I taught the -100 series back in 1977-78.

Yes, there were a couple of early landing accidents
attributed to excessive sink rates and the fix was to
change the technique that the pilots were using.

Would you like a lesson on the flap/speedbrake interaction
and the sink rates that it causes?

Bob Moore
ATP B-707 B-727 L-188
PanAm (retired)