Richard L. Gray
Consultant Riverside Research Institute
Wil L. Good
3D Research Corporation
3D Research Corporation
In response to a request from the Missile Defense Agency, Washington, D.C. and the Space and Missile Defense Command Huntsville, AL
September 21, 2002
The authors wish to thank the following people (In alphabetic order) whose recollection of the Lisa Ann renamed Rivet Amber lost over the Bering Sea were instrumental to the accuracy of this report:
* Larry Cobb
* Peter Hurd
* Bill Grimes
* Wil Main
* Don Smith
We also wish to thank the following (In alphabetic order) for providing technical input to this paper:
* Dick Dyer
* Frank Grimsley
* Phil Jones
* J.C. Kelly
In tribute to the aircrew of Rivet Amber every attempt has been made to portray the events of June 5th 1969 as accurately as possible. The authors understand the loss felt by fellow members of the brotherhood of arms and acknowledge the contribution made by the Cold War Warriors of Rivet Amber. This work is dedicated to their memory.
During June 1969 while returning from an operational flight off the east coast of the Kamchatka Peninsula, Rivet Amber experienced severe turbulence.1 Following its landing at Shemya Air Force Base, Alaska the aircraft was inspected for damage. Extensive skin damage to the tail section to include the vertical stabilizer, and areas close to the long wire High Frequency (HF) antenna tail mounts was found. No other external or internal damage that could be visually inspected was discovered, and no damage to the modified sections of the aircraft’s S-Band radome was noted. Over the objection of the maintenance crew, the aircrew was directed to fly the aircraft to Eielson Air Force Base, Alaska for additional inspection and repairs as necessary.2
The following day, June 5th, 1969 Rivet Amber departed Shemya AFB for Eielson AFB; the climb out to altitude and initial cruise appeared to be uneventful. Communications from the aircraft were normal. At approximately 1736Z, forty-five minutes into the flight SMSgt Larry Cobb flying on the Big Team aircraft picked up a distress call from Rivet Amber:
“Rivet Amber had declared a May Day and was reporting severe vibration and was descending to lower altitude.”
Subsequently, SMSgt Cobb reported receiving a second call, but he was unable to copy anything other than the call sign. A third HF transmission was reported that directed the crew to go to full oxygen. This was most likely intended to be sent over the aircraft intercom system, but was transmitted over HF.3
Tones from the HF transmitter (tuner motor) continued to be received until 1822Z. At that time all contact with Rivet Amber was lost. Later analysis of the recordings of these brief 1-3 second modulated tone transmissions by National Security Agency analysts confirmed that they were emitted from Rivet Amber. Although Rivet Amber was in a heavily traveled air corridor by both military and commercial aircraft there are no known records that indicate UHF or VHF transmissions from the RC-135E were either detected or reported.
A massive search of the area by Air and Sea assets failed to find any trace of Rivet Amber. No emergency locator beacons and no debris of any kind were ever found.
Soviet Trawlers in the area along with sophisticated Soviet ground-based long-range HF direction finding equipment may have documented the location of the crash site. Pete Hurd (one of the original RC-135E aircrew) believes it is possible that a search of the Soviet long-range HF passive detection network archives may yield data on the RC-135E crash location, although no known attempt to date has been made to validate this speculation.
History of the B707/KC-135 & Modifications to Rivet Amber
During test flights of the Boeing707 model 367-80, the prototype aircraft from which both the B-707 and KC-135 were built, the aircraft exhibited poor directional stability characteristics at low speed. No action was taken to address this problem until after several 707-100 service incidents occurred cumulating in the loss of a Braniff Aircraft in 1959.4 This mishap was attributed to Dutch-roll characteristics (lateral-directional oscillations). Improvements instituted to correct this problem were a directional stability modification to include a high aspect ratio vertical stabilizer and hydraulic powered boosted rudder controls (including a yaw damper). A separate Air Force mishap was the critical event leading to the incorporation of a hydraulic powered rudder system on the KC-135 aircraft. Although these fixes to both the B707 and KC-135 including the larger vertical tail stabilizer corrected the low speed and Dutch roll characteristics, it introduced additional stresses to the tail section of these aircraft. This resulted in the loss of a KC-135 when its tail section failed. A similar such incident involving the crash of British Overseas Airways B707 near Mt. Fuji, Japan was attributed to severe turbulence which resulted in the failure of the aircraft tail section.5 As a result, the Air Force developed the Pacer Fin modification, which corrected the stress problem by improving the tail fuselage attachment points.6
All of the fixes to the aircraft were incorporated into Rivet Amber except for the Pacer Fin modification. This left Rivet Amber with the large, high aspect ratio tail but with the original attachment system.
Rivet Amber was a highly modified radar aircraft specifically designed during the Cold War to collect radar cross-section and dynamic trajectory data on Soviet ICBM warheads and “tankage” off the coast of Kamchatka. The S-band radar was capable of detecting SS-7, 8, and 9 targets at nearly 1000 nm and could simultaneously track both penetrating warheads and any anti-ICBM launches in the target area. The modifications included the installation of a seven-megawatt (ERP) doppler radar and the removal and replacement of a 20-foot section of the aircraft’s forward fuselage skin with a conformal load bearing fiberglass-type radome. Other modification included one left wing mounted generator for the additional required electrical loads. A one million BTU heat exchanger was mounted under the right wing. These modifications caused the aircraft to appear to the casual observer to have six “engines”. All in all these modifications resulted in the heaviest and most costly RC-135 built to that date. The Pacer Fin tail fix was not included in the original or later modifications to the aircraft.
Rivet Amber departed Greenville Texas and began collecting data in late 1965; Rivet Amber flew for two years and then returned to Greenville, Texas to undergo programmed maintenance and inspection. During this maintenance period the aircraft was completely stripped and the radar modifications checked for signs of deterioration. The modified sections were X-Rayed and scoped, no chaffing or other signs of fatigue or wear were found. The aircraft was returned to the field and performed approximately 50 additional missions over the next nine months. At some point during this period an inspection of the tail was accomplished and a determination made that the Pacer Fin modification could be waived for an additional 500 hours.7 From all information available to the authors of this report regarding the Pacer Fin TCTO guidance, the RC-135E was well inside 'permitted' flight hours when lost. This again suggests that the decision by the 6th Strategic Wing authorities to fly the aircraft from Shemya was the most serious contributing factor to its loss. Interviews with LTV employees conducted (by Pete Hurd) before their death 8 indicated that the company personnel strongly objected to further flight operation of the aircraft until further interior inspections of the damaged surfaces at Shemya could be accomplished. The decision proved to be unfortunate.
FACT & SPECULATION
The authors did not have access to any official accident reports and thus any statements made are purely ours. There are few facts in this case and speculation passed on as fact is irresponsible. This much is known:
1. Rivet Amber did have the enlarged high aspect ratio vertical stabilizer
2. Similar incidents (KC-135 & B707) had shown the enlarged vertical stabilizer might have contributed to failure of the tail structure. (Shown as fact only to establish a known pattern of failure)
3. The Pacer Fin modification, which would compensate for the larger vertical stabilizer was not installed.
4. The Rivet Amber modification did replace a significant portion of the forward fuselage skin with a conformal load bearing fiberglass-like shell.
5. Rivet Amber was considered the heaviest RC-135 in the field.
6. The examination of the Rivet Amber modifications after two years of successful flight did not reveal any structural deterioration.
7. Based on an examination of Rivet Amber after its return to the field the aircraft was cleared for an additional 500 flight hours before the Pacer Fin modification was to be performed.
8. Rivet Amber had sustained visible damage to the tail section due to severe turbulence experienced the day prior to its last flight. No damage was reported to the modified section of the aircraft.
9. Rivet Amber continued flight 46 minutes after the reception of the first distress signal.
10. Three HF messages were received:
a. Experiencing severe vibration
b. Call sign only
c. Directing the crew to go to full oxygen.
11. No UHF or VHF signals were reported
12. No debris was ever found.
ALL ELSE IS SPECULATION.
Based on the stated facts it is reasonable and prudent to arrive at the most likely conclusion. The following potential causes are listed in most likely to least likely order:
1. Failure of the vertical stabilizer leading to failure of the tail section.
2. Fire caused by some mechanical means:
a. Outboard pod mounted generator or cooling systems
b. Cabin installed systems
3. Structural or mechanic failure unknown but related to the severe turbulence.
4. Stresses induced from the overall weight of the modifications transmitted to the tail section.
5. Failure of the fiberglass radome as a result of other aircraft fuselage over-stress conditions caused by the failure of the (or critical portions of the) vertical stabilizer.
The most likely cause of the loss is failure of the vertical stabilizer leading to the loss of orsevere damage to the tail section, which resulted in loss of control. This can be taken in context with the known damage to the tail noted by the maintenance crew, the absence of the Pacer Fin modification, a pattern of such failures and the evidence that points to a loss of control over time. It is obvious that the crew had some 46 minutes that they wrestled with the impending disaster. No explosive decompression was evident which tends to eliminate the loss of the fiberglass radome as a direct cause of the accident. No debris was ever found which further tends to eliminate the explosive decompression or breakup of the aircraft theory.
The fire theory originated from the pilot’s call for the crew to go to full oxygen. However, this call may have been the result of a sudden loss of cabin pressure or some other problem necessitating this action. Many reasons have been put forth for this call but all are speculative in nature.
Structural or mechanical failure related to severe turbulence. This again would lead one to believe the tail was the first such area of the aircraft to fail. Visual damage had been reported and the aircraft was returning to Eielson AFB for inspection and repair to the tail section. It is reasonable to conclude that if this failure mode were to be assumed, the tail section would be the most likely place where the structural failure took place or would begin.
Failure cause four is looked upon as a contributing cause. The stress transmitted to a weakened tail from the overall weight of a heavy aircraft could conceivably exacerbate the problem. Because of an over two-year history of success this is not considered a primary cause, but is a likely contributor.
Finally, a failure of the fiberglass radome would certainly have caused instantaneous catastrophic aircraft loss. This is considered the least likely cause for the following reasons:
* No damage was reported to this section by the maintenance crew at Shemya after the sever turbulence incident
* A loss of a 20 foot section would not allow a 46 minute continuation of the flight, as the radome was a load-bearing member of the fuselage, its complete or partial loss would have induced radical fuselage bending and surface fuselage skin ruptures.
* After two years of flight, the last maintenance period at Greenville, TX indicated no deterioration of the modification during careful inspection as required by the Pacer Fin technical directive.
* No spread of debris was ever found.
Everything that was found about this accident indicates severe damage to the aircraft tail section, which resulted in loss of control. The aircraft, debris or any other evidence that could refine the cause of the crash was never found. This leads to speculation and nothing more. In fact, no cause was ever determined nor have we determined a cause of this event.
The loss of the RC-135E Rivet Amber was most likely from the loss of control resulting from extensive tail damage. Damage to the tail was initially the result of severe air turbulence, which likely further weakened the connecting structure of the vertical stabilizer to the tail section of the fuselage. All accidents tend to be a chain of such unfortunate events. Had Pacer Fin been installed, had the aircraft not met with sever turbulence or had the modifications not significantly increased the weight of the aircraft and had the aircraft been grounded at Shemya, AFB this might not have happened.
Extrapolating this knowledge to the Widebody Airborne Sensor Platform (WASP) is at best a stretch and at worst an attempt to pass speculation off as fact in an irresponsible manner. However, since 1969 design and construction of highly modified aircraft has evolved and improved. Although nothing is without risk and with each advance comes new risk, the DC-10-10 has been modified within a fail-safe philosophy. In order to minimize the potential of a structural failure which could result in an instantaneous catastrophic condition (The authors were led to believe that this is the concern voiced by the individual prompting this report) the DC-10-10 design requires that the adjoining belt frames be designed to support a failed belt frame such that the overall integrity of the modification will be maintained without any deleterious effect on the aircraft.
1. FAA Airman Information Manual, 7-1-23, Severe Turbulence is defined as: Large, abrupt changes in altitude and/or attitude. Causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about.
2. Comment from Pete Hurd: This is a very emotional issue with some of the surviving (LTV-era) personnel. They were walking a very fine line with both the company's 'can-do' attitude of that time, and contractor insubordination. On the other hand, who would not want a 'free ride' to civilization, particularly if your military family was waiting for you there? This report is intended to honor those who looked a possible disaster straight in the face, saluted, climbed aboard the bird, and started engines. I lost several good friends in the crash. My later interviews with USAF HQ staff-members who were close to the top USAF leadership indicated that this aircraft's loss ranked up there with the U-2 shoot-downs as to senior leadership attention/impact.
3. Mr. Wil Main reported that FAA Air Traffic Control, and Commercial Aircrews in the area reported monitoring and recorded these HF distress calls.
4. The reader is referred to http://www.braniffinternational.org/aircraft/accidents.htm
5. The reader is referred to: http://www.kembleairrace. freeola.com/PILOTFRIEND/disasters/911%20crash.htm
6. The reader is referred to: www.tinker.af.mil/pa/archive/2001083/kc-135.htm
7. According to Dr. James Crowder, Historian at Tinker AFB, the Pacer Fin TCTO 772 was an interim inspection for C-135 type aircraft, to be followed by TCTO 775, which would have modified the RC-135E tail fin. The TCTO 772 inspection action is noted by Tinker records as having been “…inspected by LTV at Greenville, TX on 1968 August 10." At that time a reported 2960 hours of flying time had been logged on the aircraft, thus placing it in “Category-II” which permitted between 500-1200 operational hours on the airframe. Based on this assumption, the RC-135E was scheduled to receive the TCTO 775 modification during September 1970. The aircraft was lost after flying a reported 390 hours after the inspection.
8. Death not related to Rivet Amber.