54 MAY 2020 ÇPlane&Pilot
degrees of flaps, the stall speed is reduced to 98 knots
calibrated airspeed.
Investigators plotted four takeoff paths using
Runway 3 and found that the only way the airplane
likely would have had sufficient climb performance
to clear terrain would have been if it made the same
right turn as the airplane that had previously taken
off, instead of the left turn the accident aircraft made.
There was an official weather observation station
located about 25 miles east of the accident site. The
observation recorded about four minutes after the
estimated time of the accident included wind from
about 090 degrees at 4 knots gusting to 12 knots. The
station was at 128 feet MSL while the Islita Airport
was at an elevation of 65 feet MSL. The elevation of
the accident site was 238 feet MSL.
The airline was supposed to have provided special
training for pilots who fly into and out of unusual or
difficult airports, according to its General Operations
Manual. The NTSB’s report did not verify whether
that had been done with respect to the Islita airport,
since investigators said there was no list naming the
airports for which special training would be required.
The Caravan was powered by a Pratt & Whitney
Canada PT6A-114A turboprop
engine rated at 675 horsepower. It
used a constant-speed, full-feath-
ering prop, which had reverse pitch
capability. The airplane had 12 pas-
senger seats plus the two pilot seats.
The airplane originally was given an
experimental airworthiness certifi-
cate in 2001 because it was going to
be used for research and develop-
ment. An export application was filed
in November 2011 showing Nature
Air had bought it. In June 2016, it
was issued a normal category FAA
airworthiness certificate after having
been shipped back to the U.S. In November 2017, it was
again exported to Costa Rica, with Nature Air shown
in official documents as the purchaser.
Records for the airplane showed that at the time
of the accident, it had accumulated 12,072 hours in
service with 20,813 cycles. The engine had accumu-
lated 3,271 hours and 4,637 cycles at the time of the
accident. Investigators noted that when the airplane
flew into Islita to pick up passengers, it had suffered
a bird strike that caused localized damage on the
leading edge of the left wing near the landing light.
A photograph taken by a passenger on the inbound
flight showed that the landing light lens was cracked
and the leading edge adjacent to the light was slightly
deformed. The Safety Board reported that due to the
localized nature of the damage, the airplane’s flight
characteristics and controllability would not havebeen affected. A witness told investigators that the
reason for the accident airplane not taking off until
15 minutes after the first 208B had departed was
because the captain wanted to wait for a release from
maintenance regarding the bird strike damage.
The wreckage had been removed from the accident
site before the NTSB investigators arrived on-scene,
but they were able to examine it later. It was broken
into numerous pieces and showed extensive fire
damage. No flight or engine instruments could be
identified. Examination of the engine by investiga-
tors found evidence consistent with it having been
operating at impact.
The NTSB reported that investigators did not
receive information about the first officer’s medical
history but did receive limited medical information
about the captain. It showed that the pilot had a history
of Type I bipolar disease, attention deficit disorder and
a history of treatment with a sedating antipsychotic
and antidepressant earlier in life. The NTSB reported
that on his applications for Costa Rican and FAA
medical certificates, he generally reported no visits
to health care providers, no use of medications and
no chronic conditions.
The NTSB determined that the
probable cause of the accident was
the flight crew’s failure to maintain
airspeed while maneuvering to
exit an area of rising terrain, which
resulted in exceeding the airplane’s
critical angle of attack and aero-
dynamic stall. Contributing to the
accident was the flight crew’s deci-
sion to continue the takeoff toward
rising terrain that likely exceeded the
airplane’s climb capability, the lack of
adequate weather reporting available
for wind determination, and the lack
of documented training for an airport
requiring a non-standard departure.
One of the important lessons pilots should learn
about operating around high terrain is to be conserva-
tive when making judgments about the aircraft’s ability
to climb fast enough and at a steep enough gradient
within the proper flight envelope to clear terrain. The
terrain isn’t going to move out of your way, so you have
to plan how you’ll get around it. Why the pilots of flight
9916 missed something so basic remains unresolved
despite Costa Rica turning the investigation over to
the NTSB. PPPeter Katz is editor and publisher of NTSB Reporter, an independent
monthly update on aircraft accident investigations and other news
concerning the National Transportation Safety Board. To subscribe, visit
http://www.ntsbreporter.us or write to: NTSB Reporter, Subscription Dept., P.O.
Box 831, White Plains, NY 10602-0831.❯ ❯ “The airline was
supposed to have provided
special training for pilots
who fly into and out of
unusual or difficult airports,
according to its General
Operations Manual. The
NTSB’s report did not verify
whether that had been
done with respect to the
Islita airport.”