Page 15 - Forum-2021-JanToMarch

Image Analysis of Video Taken on the with trees when the video recording stopped
Helicopter with the impact of the helicopter crashing
Since the helicopter was not equipped with into the ground.
a recording device such as a black box, it
was difficult to determine fact information. Lesson 4: Analysis of flight tracks from video
However, the camera attached to the rescuer’s taken on the helicopter.
helmet was taking a video of the situation
from the middle of flight until the accident. Detailed Investigation of the Helicopter
The video shows that the weather at the time From the scattering of debris from the acci-
did not interfere with the flight. dent site, it was estimated that the helicopter
The helicopter gradually approached the hit a tree and became uncontrollable and
mountain surface covered with trees at a crashed. The investigation of the details of
constant attitude and speed and crashed into the airframe was conducted in June when
trees. That the helicopter was flying normally the snow melted and the debris was salvaged
and then, without an avoidance maneuver, from the mountain, and no anomalies of the
collided with trees as it gradually approached airframe and engine were found from the
is highly unusual. What happened? Nothing debris.
happened. Why did the pilot fail to avoid? This
was a shocking question that I had to keep
asking until the end of the investigation. Voice Analysis of Video Taken on the
Estimating the position and altitude of the Helicopter
helicopter over time by analyzing still images An alarm sound and sounds indicating ab-
with the video stopped and then estimating normality of the helicopter were not recorded
the flight path by linking the images was until it collided with trees. A sheet recorded by
possible. We knew that the helicopter took a mechanic sitting in the left seat was found,
off from the airport, headed northeast while which revealed that the crew of the helicopter
climbing above the city, entered the airspace had been performing engine performance
above the mountains, and turned right. It is tests after takeoff.
highly probable that it headed toward Mt. Furthermore, by combining and analyzing
Hachibuse in continuing roughly level flight this one sheet and the in-flight video and
at a speed of about 100 knots. The helicopter’s audio, the in-flight situation became clearer.
altitude above ground level (AGL) became At first, I had no idea what the crewmem-
lower gradually, and the tree-covered moun- bers were talking about, but it became clear
tainside was looming ahead. The helicopter that they were checking the engine, and the
collided with trees while maintaining attitude content of the conversation became more un-
and speed. derstandable. Furthermore, by analyzing the
The helicopter leveled off at about 1,740 engine noise, it was possible to estimate the
meters. It is somewhat likely that this was be- throttle and engine N2 governor operation
cause the helicopter was trying to ensure the status during engine check, which supported
safety altitude of 150 meters or higher from the fact that an engine check was performed.
the destination, the helipad, with an elevation An analysis of the audio recorded by the
of about 1,580 meters. It is highly probable video camera found that a spectrum of ap-
that while maintaining the maximum safety proximately 22 Hz was recorded at a constant
altitude, the helicopter took neither the avoid- frequency from the beginning of the video
ance route at a constant altitude by directly until 4.0 seconds before the audio recording
heading for the helipad nor the avoidance stopped. Assuming that the sound was gener-
route by climbing. Instead, it continued to fly ated by the MRB, this would be equivalent to
toward Mt. Hachibuse at a constant altitude approximately 330 rpms. The 100% number of
after turning right. Its AGL became lower MRB revolutions is 324 rpms.
while flying into and over the mountains An audio spectrum of approximately 3,300
region, and the helicopter approached the Hz and an audio spectrum of approximate-
ground. It is highly probable that the helicop- ly 3,400 Hz were transmitted at a constant
ter flew into an uncontrollable condition as frequency, respectively. However, immediately
it crashed its fuselage and main rotor blade after the voice of “minus two,” in the former
(MRB) into trees over a distance of approxi- case, the frequency increased by approximate-
mately 40 meters. It is highly probable that the ly 200 Hz, while in the latter, the frequency
helicopter turned upside down and collided decreased by approximately 200 Hz. Those
with an approximately 40-degree slope from frequencies returned to original frequencies,
its nose. It is also highly probable that it was and they were constantly transmitted again, Koji Fukuda
four seconds later after the helicopter collided immediately after the voice saying, “I return it.”
January-March 2021 ISASI Forum • 15