Hiram
1971-JAN-07 · Lake Michigan, near Charlevoix, Michigan

United States Air Force — Flight Hiram 16

A United States Air Force B-52C Stratofortress, call sign Hiram 16, suffered a catastrophic structural failure of its left wing during a low-level training mission over Lake Michigan. The aircraft was participating in a Radar Bomb Scoring (RBS) exercise on the Olive Branch 9 (OB-9) route when the left wing snapped between the two engine pods due to metal fatigue. The bomber plunged into the water and exploded on impact, killing all nine crew members. The accident highlighted the severe structural stresses placed on the B-52 fleet, which had been designed for high-altitude flight but was repurposed for low-level penetration missions to evade Soviet surface-to-air missiles.

Aircraft
Boeing B-52C Stratofortress
Registration
54-2666
Phase
Cause
Souls on Board
9
Fatalities
9
Origin → Dest
Westover Air Force Base, Massachusetts → Westover Air Force Base, Massachusetts
Report

Investigation Summary

The B-52C involved in the accident was 15 years old and had not been structurally modified to handle the increased turbulence and air density of low-level flight. On the day of the accident, the crew was performing a Combat Crew Training Mission that included a practice refueling and four simulated bomb runs. During the first refueling attempt, the crew reported a minor hydraulic leak but elected to continue the mission, skipping the second refueling. Weather at the time consisted of broken to overcast skies at 2,500 feet, visibility of two miles in light snow, and rime icing in clouds from 2,500 to 6,000 feet. The aircraft prepared for its scoring runs at an initial altitude of approximately 700 feet, but due to the cloud ceiling, it descended to between 300 and 500 feet above the water for the final runs. While initiating the run on target Charlie after successfully hitting target Delta, the aircraft suddenly disappeared from radar. Witnesses on the shore reported a massive fireball, comparing it to a sun rising in the northeast. Recovery efforts were delayed by winter ice, but salvage operations in mid-1971 retrieved the engines and wing sections from a depth of 225 feet. Analysis of the wreckage confirmed that the main wing spars had succumbed to fatigue, leading to the total separation of the wing.

Final Conclusions

The United States Air Force Accident Investigation Board concluded that the primary cause was the structural failure of the left wing spars due to metal fatigue. The board noted that the B-52C models were being operated in a low-level environment for which they were not originally designed, leading to accelerated fatigue in the wing structure. The investigation also confirmed the aircraft was not carrying nuclear weapons at the time of the crash.

Video Analysis

No video analysis linked for this case file yet.

Airframe & Maintenance

Airframe Hours
0

Crew Experience

Aircraft Commander

Total hours
4,469
On type
3,127

Lt Col William Lemmon

Systems & Failure Modes

i

Wing Spars

The primary structural members of the wing which failed due to metal fatigue, leading to the separation of the left wing between the engine pods.

i

Radar Bomb Scoring (RBS)

Ground-based electronic equipment used to track the bomber and simulate the accuracy of bomb drops and electronic jamming effectiveness.

Interesting Facts

  • 01The aircraft initially prepared for scoring runs at 700 feet but was flying at an altitude of approximately 300 to 500 feet above the water at the time of the failure.
  • 02The crash occurred only 5 miles north of the Big Rock Point Nuclear Power Plant, which had previously expressed concerns about low-level overflights.
  • 03No human remains were ever recovered from the crash site.
  • 04The B-52C was traveling at approximately 365 mph (317 knots) when the wing failed.
  • 05The aircraft was one of only 35 B-52C models built, all of which were stationed at Westover AFB by 1971.

Safety Actions & Advisories

Low-Level Flight Restrictions

The accident reinforced the need for structural reinforcement programs for the B-52 fleet to handle the stresses of low-level 'Oil Burner' routes.

Location

Lake Michigan, near Charlevoix, Michigan · 44.0000, -87.0000

Case File History

  1. CorrectionUpdated investigation summary.
  2. CorrectionUpdated investigation summary.

Related Cases

Case ID · b52-lake-michigan-1971Last updated · Filed

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