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Forensic Acoustics Technology

Beginning April 12, 2002, I conducted tutorials at local detention centers on the subject of HTML. My spouse, Nancy, helped detainees select reading materials. We concluded our volunteer efforts in the Spring of 2006.

The purpose of this site is to encourage others to become interested in Forensic Acoustics Technology.

The authors of this page are me, Glenn Bowie, and my friend Craig Melvin. You see Craig at Air Force Plant 42, Palmdale, California. He is controlling our field assistant, miniature schnauzer Brandy. It is the summer of 1970.

By May 1986, Craig was a leading Forensic Acoustics Technologist. He was a Deputy in the Los Angeles County Sheriff's Department.

My wife, Nancy, and I measured flyover and flyby sounds during landing approach of B-727-200 at Palmdale Air Force Base, California, on 30 occasions in the summer of 1970.

Craig Melvin operated a micrometeorologic tower facility to measure wind speed and temperature at heights above the ground from 5 ft. to 50 ft. during the tests.

e-mail, Jan. 21, 2006
Glenn,
I was scared to death the first time I climbed the oil tower at the back of Rye
Canyon. That is when I found the instruments used at Palmdale. Other workers
took them down from the tower.

I believe that Sullivan was the one that helped to hook it all up.

I remember being just before the touchdown at Palmdale with reflective
microphones in the first flyover noise acquisition.

Did not know what I was doing. But a lot of fun.

I watched Sullivan pore over calculations to be sure that we were measuring the
temp measurements from the tower rather than heat sensitive resistance in the
wires lying on the desert floor.

Lets do it again.

Craig.

Craig is holding the flashlight. We were recording sounds while LASD deputies and explosive experts initiated pyrotechnic effects.

Craig is now a Detective Sergeant, Homicide Division, Los Angeles County Sheriff's Department. Our relationship shows how varied experiences can be applied to solve particular forensic acoustics problems.
Indian Dunes
Craig joined the Los Angeles County Sheriff's Department (LASD) as a deputy. In December 1980, he obtained permission for me to use acoustic test equipment owned by my employer, the Lockheed California Company, to measure sound levels near the ears of a lead Swat Team Member during a practice forced entry of a building. Swat Team Exercise

>

The changes in pitch you hear when playing the above aircraft flyby sound are described as Doppler frequency shifts.

On July 22, 1982, actor Vic Morrow was carrying two children across a pond at a movie set. The location was Indian Dunes, Valencia, California. Pyrotechic effects were initiated to heighten drama of the scene being video taped. A helicopter hovered above them.

Vic Morrow and the one child were killed when struck by the helicopter main rotor. The right skid struck the second child and killed her.

What happened? To an aircraft engineer, an "Aircraft On The Ground" or "AOG" event occurred. This term is used to denote a catastrophe. Pilot Dorsey Wingo, Western Helicopter Company, was operating a Bell UH-1 Huey according to a script. He also followed directions of episode Director John Landis. The latter was standing in the pond, below the helicopter, in sight of Dorsey Wingo. He was using his right arm in a repeated gesture indicating he wanted the helicopter to come lower. He was yelling "Lower, Lower, Lower" while gesturing. Special effects explosions were occurring.

I analyzed the soundman's tape recording. The recording was made on a Nagra reel to reel machine. I had access to the same type of recorder used by the soundman. I identified the sound of the tail rotor striking the surface of the pond. The rotational sound of the tail rotor stopped on impact. I tracked the rotational sound back to the original position of the rotor at the helicopter tail section.

In aircraft industry folklore, "an act of God" is an event involving a major structural failure. Separation on a wing from an aircraft is an example. A pilot cannot be expected to control flight under such a condition. Dorsey Wingo could not be expected to control the Huey after the tail rotor separated.

It remains to ask "Why did the rotor separate?". I am on shakey ground here. If memory serves, I think I found that a shear pin failed. The pin secured the rotor to the rotor drive shaft. It was a structural failure of a pin that caused the rotor to separate. Why did the pin fail? It could have been a combination of a fatigue failure and an overload failure. Or it might have been an overload failure. Presumably an overload could have been caused by hot gases from an explosion, or by a sudden maneuver, or both. I wrote a report about my findings. Perhaps a copy could be found in LA Sheriff's Department archives. I do not have a copy.

E-mail message received on February 7, 2002, from Larry Tabert:

Hi Glenn,

I glanced at your link this morning, didn't have time to answer you. I haven't flown a UH-1 in over 12 years. In Viet Nam, I used to maintain them, but that was a long time ago. I retired from the Army in 1993, last flew Blackhawks (UH-60). I participated in many aircraft accident investigations in my 23 year army career and also did a stint as a police officer in Clearwater Florida, so I understand the necessity for solid investigational techniques.

To the best of my recollection, the tail rotor hub, which the two blades were attached to, fit on the spindle that came out of the tail rotor gear box. It was kept from slipping by the mated splines on the spindle and the hub. The hub slid onto the spindle and the splines kept the hub tight on the spindle to ensure it didn't slip as the spindle turned the hub and blades. Once the hub was on, I was held tight on the spindle by a nut that was safety wired to ensure it didn't come loose, the nut being tightened to a specified torque.

I am a member of an internet mail list of Viet Nam Pilots and Crew Chiefs. I can ask, I am sure others may be able to provide more information on this subject. If you'd like, I'll forward your message to the net.

Just curious, how did you come across my name?

Larry Tabert

I was on shaky ground. No shear pin existed in the tail rotor assembly. Now I wonder how the hub slid free of the splines on the spindle. Details of the maintenance of nut torque and inspection of the safety wire would be valuable.

Images and specifications of the Huey UH-1 helicopter may be seen at:
http://www.fas.org/man/dod-101/sys/ac/uh-1.htm

On February 7, 2002, I received the following e-mail from Jim Self, who is an animation artist with strong interests in aviation.

Hi Glenn,

....I can see where your skills could be used in accident investigation work....

I do push a good broom.

I don't see any problem using that image, but then I'm not sure where it came from either. I'm using it too so don't worry much about it.

---==X={}=X==---

Jim Self

AVIATION ANIMATION, the internet's largest depository. http://avanimation.avsupport.com

Your only internet source for spiral staircase plans.
http://jself.com/stair/Stair.htm

AGAG panel member, Animated Gif Artists Guild
http://agag.com

The discussion about UH-1 animated images has sparked some fresh thoughts about Twilight Zone events at Indian Dunes. Positions of the Director, helicopter, and special effects could be illustrated. The gesturing director, initiation of explosions, and possible effects on the tail rotor could be animated.

On February 4, 2002 I communicated by phone and e-mail with Craig Melvin. He is not active in law enforcement at this time. His e-mail response follows.

Glenn, Saw the site. Wow, what a flashback.
Thanks for the memories. I have to go right now, but the section on the tail rotor etc. needs a little fine tuning. The issues were whether heat from a delayed explosion delaminated the tail or whether a flying missle from the ground explosions impacted the rotor on the back side.

Give me some time to get back home and I will send some comments.

Craig

On February 4, 2002 I communicated by e-mail with the National Transportation Safety Board, NTSB. On February 5 I received a reply from NTSB representative Carter Latricia. His e-mail letter included a summary accident report about the Twilight Zone event. A portion of that attachment is included below.

Brief of requested accident. -----Original Message----- From: Glenn Bowie [mailto:jailprogramvolunteers.org]
Sent: Tuesday, February 05, 2002 6:26 AM
To: avdata@ntsb.gov
Subject: Twilight Zone Trial

Dear Madam or Sir,
I worked on the 1982 case in which Vic Morrow and two children were killed. I understand there was an NTSB investigation.

My work concerned sounds recorded during the Indian Dunes Twilight Zone episode.

Would the NTSB Report give me any help concerning the way the Bell Huey tail rotor parts were assembled? I am particularly interested in the attachment of the rotor hub to the rotor shaft.

Sincerely,

Glenn Bowie

PORTION OF NTSB SUMMARY REPORT

------------------------------------------------------------------------------------------------------------------------------------ ----Narrative---- ACFT BEING USED TO FILM MOVIE SCENE DEPICTING ATTACK OF VILLAGE TYPICAL OF VILLGES IN VIET NAM. ACFT WAS ABOUT 25 FT AGL & ABOVE LOCATION WHERE SPECIAL EFFECTS EXPLOSIVES WERE DETONATED. AS THE PLT TURNED ACFT FOR CAMERA COVERAGE, ACFT'S TAIL SECTION WAS ENGULFED IN FIREBALL CREATED BY SPECIAL EFFECTS EXPLOSION. T/R ASSEMBLY SEPARATED & ACFT DESCENDED OUT OF CONTROL. M/R BLADE STRUCK 3 ACTORS ON GROUND. THE BOARD DETERMINED THAT THE PROBABLE CAUSE OF THE ACCIDENT WAS THE DETONATION OF A DEBRIS-LADEN SPECIAL EFFECTS EXPLOSION TOO NEAR THE ACFT. THE PROXIMITY OF THE ACFT TO THE EXPLOSIONS WAS DUE TO THE FAILURE TO ESTABLISH DIRECT COMMUNICATIONS & COORDINATION BETWEEN THE PILOT, WHO WAS IN CHARGE OF THE ACFT OPERATION, & THE FILM DIRECTOR, WHO WAS IN CHARGE OF THE FILMING OPERATION.
------------------------------------------------------------------------------------------------------------------------------------ PAGE 1

Brief of Accident (Continued)

File No. - 2915 7/23/82 VALENCIA,CA A/C Reg. No. N87701 Time (Lcl) - 0220 PDT ------------------------------------------------------------------------------------------------------------------------------------

Occurrence #1 AIRFRAME/COMPONENT/SYSTEM FAILURE/MALFUNCTION
Phase of Operation MANEUVERING

Finding(s)
1. AIR/GROUND COMMUNICATIONS - NOT PERFORMED - PILOT IN COMMAND
2. AIR/GROUND COMMUNICATIONS - NOT PERFORMED - GROUND PERSONNELM
3. CREW/GROUP COORDINATION - NOT PERFORMED - PILOT IN COMMAND
4. CREW/GROUP COORDINATION - NOT PERFORMED - GROUND PERSONNEL
5. ROTOR SYSTEM,TAIL ROTOR BLADE - FOREIGN OBJECT DAMAGE
6. ROTOR SYSTEM,TAIL ROTOR BLADE - BURNED
7. ROTOR DRIVE SYSTEM - VIBRATION

------------------------------------------------------------------------------------------------------------------------------------ Occurrence #2 LOSS OF CONTROL - IN FLIGHT
Phase of Operation MANEUVERING

------------------------------------------------------------------------------------------------------------------------------------ Occurrence #3 IN FLIGHT COLLISION WITH TERRAIN
Phase of Operation DESCENT - UNCONTROLLED

------------------------------------------------------------------------------------------------------------------------------------ Occurrence #4 PROPELLER/ROTOR CONTACT
Phase of Operation DESCENT - UNCONTROLLED

------------------------------------------------------------------------------------------------------------------------------------ ----Probable Cause----

The National Transportation Safety Board determines that the Probable Cause(s) of this accident is/are finding(s) 1,2,3,4

I think the group photo was taken in 1986 or thereabouts. It includes program C.A.V.I.S. participants and supporters. I am on the left end, Lonnie Smrkovski is on my left, and Craig Melvis is beside Lonnie. LA County Sheriff Sherman Block is at back row center, wearing glasses. Dr. Hiro Nakasone is in front of Craig and Sheriff Block.

Craig is occupied full-time now with his boat handling business. On February 10, 2002, he sent an e-mail message containing memories of the Twilight Zone investigation.

Hi Glenn,

Just got back in and e-mailed Lonnie.  You have gotten old friends together.
Thanks.

The tail rotor was made up of laminates which separated.  Some felt that the
heat from the delayed explosion cause the tail blade to separate.  Think of
it as layers of plywood.  One of the explosions did not explode normally.
The pots were shaped either cylindrical or conical.  Sawdust soaked in
gasoline was in the pot and a detonation device set it off.  When helicopter
was over the crucial explosion the gasoline did not ignite right away.
Instead, the wet gas was propelled upward around the tail rotor and then
exploded.  The heat from this delayed explosion was one theory.

The other theory was that because there was a dent on the back side of the
rotating tail blade it was thought that a piece of bamboo from the stage
huts flew up and struck the rotor.  This collision was thought to unbalance
the rotor and tear it loose from the tail structure.

Others argued that the tail rotor was going so fast that nothing could catch
up to the back edge.  Think of a baseball picture trying to hit the back of
a batters swing by throwing a ball from behind home plate.

I am not making anything new up.  The above is what people talked about.

The acoustic work found the delayed explosion.  No one knew about it before.
When I went to the FBI,  we sychronized the sound frame by frame.  I captured
the extra delayed explosion which could be seen for the first time on the
single frame 35 mm film.

Bamboo was shot at the Los Alamos firing range with high speed photography
to measure its velocity.  This showed that the velocity was not fast enough
to catch up with the rotor.

Another opinion was that a piece of bamboo could be twirling like a baton
going upward from the ground explosion and have its own whipping action.
All that was needed was for the two rotating bodies to meet at the right
time.

To this date, no one (in my opinion) knows exactly what caused the tail
rotor to dislodge from the tail assembly.  It was either hit and unbalanced,
or delaminated by the heat.

Once the tail rotor came loose the helicopter went out of control.

The sound analysis  could distinguish the main engine rpm which was OK.  The
main rotor was also OK.  I cannot remember the frequency now.  I believe the
engine was 10,000 rpm.

The tail rotor was the lower frequency.

During the test after the accident of the same type of helicopter, the sound
could distinguish a right or left pedal movement of the tail due to Doppler
shift.

During the whiteout effect of the filming the sound analysis could reveal
what was going on with the tail rotor.  The rpm of the tail rotor started to
wind down right after the delayed gas explosion.

The sound analysis revealed:

The helicopter main engine was OK
The main rotor was OK
The type of explosions used was verified.
The ( I believe the fifth) explosion was delayed.
The tail rotor rpm began to rapidly decelerate after the delayed explosion.


This is as much as I can remember right now.  I just got home from the
Marina.  Winds were big, but still warm.  I am doing woodwork/engine work
and electronic stuff.

Found out that an old radar is interfering with the GPS reception of a new
unit.

Going to send your url to some close friends to show them that I didn't
always have grey hair.


Anyway,  that's it for now.

Craig

References:
1. Los Angeles Times, METRO, Valley Edition, pp. 1, 3.
2. Los Angeles County Sheriff's Department, Star News, Sept. 1988, p. 27.
3. The Lockheed Star, April 10, 1986, p. 4.
4. National Transportation Safety Board, Brief Brf03.txt, File No. - 2915.
Received by e-mail from NTSB avdata@ntsb.gov, February 5, 2002.
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Craig and Pegi Melvin spent three months in the Spring/Summer of 2003 cruising from LA to Friday Harbor, San Juan Islands, Washington. They are enjoying rewards of retirement.

Beginning January 2006, we have been exchanging video clips and still images. Here are some examples. Craig uses his forensic skills when critiquing details of sounds and images I send him.

SHARE WITH CRAIG AND PEGI MELVIN: The LIME KILN STATE PARK --
Glenn, Here you can click on "listen to live" and here things as they are happening. I drop a hydrophone and amplify the sounds throughout the boat. Other boat engine noise is heard often. Craig http://orcasound.net/lk/?gmaplk

Glenn E. Bowie, CorTech Training,
Red Wing, MN. All rights reserved. When last edited: August 5, 2003. The page was first posted on February 4, 2002.