Critical Analysis of United Airlines Flight 173
James M. Oyler
School of Aeronautics, Liberty University
AVIA 400: Aviation Human Factors
Professor Aiden Van Pelt
April 1, 2024
Critical Analysis of United Airlines Flight 173
This manuscript is a critical analysis of the findings based upon the National
Transportation and Safety Board’s (N.T.S.B.) investigation and subsequent accident report. The
following information will identify all the pertinent facts related to the primary cause of flight
178’s demise. The history and qualifications of the flight crew, the type of aircraft, and the route
flown. We will identify and discuss points of interest that were not expounded on by the
N.T.S.B.’s final report. Another purpose of this research is to educate readers on risk
management procedures as they relate to sound aeronautical decision making for experienced
and inexperienced aviators.
The National Transportation and Safety Board oversees and governs all aviation
accidents in the United States. They are tasked with this mission to maintain the system of
checks and balances along with maintaining the integrity of the facts while issuing a nonpartisan
investigation, review, and determination on the cause of aviation accidents. They are judge and
jury as to where the blame is to be credited either due to pilot or flight crew error, mechanical
failure, which include any other condition that might contribute to an aviation related accident.
The NTSB’s can trace its origins to the Air Commerce Act of 1926, in which the United
States Congress charged the U.S. Department of Commerce with investigating the causes of
aircraft accidents. That responsibility was later transferred to the Civil Aeronautics Board’s
Bureau of Aviation Safety upon its creation in 1940. However, in 1967, Congress chose to
consolidate all U.S. transportation agencies into a new entity titled the U.S. Department of
Transportation (D.O.T.) and established the N.T.S.B. as an independent agency within the U.S.
D.O.T. When the N.T.S.B. was created, Congress envisioned that a single organization with a
clearly defined mission could more effectively promote a higher level of safety in the
transportation system better than individual agencies could working individually. Since 1967, the
N.T.S.B. has investigated accidents, crashes, and other events in the aviation, highway, marine,
pipeline, and railroad transportation environments, as well as those related to the transportation
of hazardous materials such as nuclear waste. In 1974, Congress reestablished the N.T.S.B. as a
separate entity outside the United States Department of Transportation, reasoning that “no
federal agency can properly perform such [investigatory] functions unless it is totally separate
and independent from any other agency of the United States”. In 2022, the investigation of
accidents in commercial space transportation was added to their mission. (NTSB, 2017)
Flight History
On December 28, 1978, United Airlines, Inc., Flight 173, a McDonnell-Douglas DC-8-61
(N8082U), was scheduled to fly from the John F. Kennedy International Airport in New York
City to the Portland International Airport in Portland, Oregon. The flight plan also called for one
stop along its route at Stapelton International Airport in Denver, Colorado. (MCA, n.d.) Flight
173 would depart from Denver about 14:47 Zulu with one hundred and ninety-eight (198) souls
on board, including six (6) infants, and eight (8) crewmembers. The flight was cleared to
Portland on an Instrument Flight Rules (I.F.R.) flight plan. The planned route time was two (2)
hours and twenty-six (26) minutes. The planned time of arrival at Portland was estimated for
17:13 Zulu. The total amount of fuel required for the entire trip was thirty-one thousand nine
hundred (31,900) pounds of fuel. The N.T.S.B. report states that United Flight 173 departed
Denver’s Stapleton Internation Airport with forty-six thousand seven hundred (46,700) pounds
of fuel on board. Note that the time of the events listed is based on a twenty-four (24)-hour clock.
(National Aircraft Accident Report, 1979)
As United Flight 173 began its final approach into Portland International Airport, the
crew began the before landing checklist procedure after calling the air traffic control and
informing them that Flight 178 was descending from ten thousand feet altitude where they had
the airport in sight. As the air traffic controller directed the aircraft to descend to an altitude of
six thousand (6,000) feet, landing preparations were being made. Following their checklist, the
crew slowed the aircraft by lowering their flaps followed by lowering their landing gear and it
was at this point where things began to go wrong for the crew and passengers onboard.
As the landing gear lowered the crew heard an uncharacteristic thump then immediately
noticed a landing gear warning light come on that warns pilots that something is wrong with their
landing gear system. The captain then contacted air traffic control (A.T.C.) to say that they were
experiencing a malfunction and would need to enter a holding pattern while they sorted out the
issue. The air traffic controller issued a vector to enter their holding pattern and as the crew was
running the emergency checklist, they found themselves approximately twenty (20) nautical
miles from the airport at an altitude of seven (7) thousand feet. The crew which consisted of the
captain, first officer, and flight engineer, would spend twenty-eight (28) minutes trying to resolve
their perceived issue.
During this time, the aircraft was configured for landing, and the pilots were not aware
that their landing gear was down and locked, causing tremendous drag on the airplane relating to
accelerated fuel consumption. As Flight 173 was ready to make its final descent to their assigned
runway the flight engineer informed the captain that they had three thousand (3,000) pounds of
fuel remaining or one thousand pounds for each engine. The aircraft was seventeen (17) miles
from the airport still in the oval shaped holding pattern which would bring them as close as five
(5) nautical miles during each circuit. Once the engineer declared the remaining fuel, the captain
realized it was time to proceed directly and without delay. However, this was too little too late
and as the flight began its final descent, they lost the first engine. At this point, the aircraft was
nineteen (19) nautical miles turning to line up for runway two-eight left (280L). The captain
instructed the flight engineer to open the cross-feeder lines on the fuel system once he realized
the gravity of the situation.
The first officer was the first to declare that the second engine was flaming out and when
the captain asked “why”, the first officer replied, “fuel”. At twelve (12) nautical miles, Flight
173 lost two (2) of their four (4) engines. Seventeen (17) seconds later they lost all four (4)
engines due to fuel starvation. The captain instructed the first officer to make the May Day call
and the aircraft impacted the ground only six (6) nautical miles from the threshold of runway
twenty-eight (28) left.
United Flight 173 came down into a wooded section of a populated area of suburban
Portland neighborhood. The wreckage path was one thousand five hundred and fifty-four (1,554)
feet long and one hundred and thirty-four (134) feet in width. There was obviously no post-crash
fire, which is one of the only positive outcomes of this accident sequence. The accident occurred
during darkness, making it difficult to locate and evacuate passengers. The flight destroyed two
homes which, at the time, were fortunately unoccupied. Ten (10) of the one hundred and ninety-
eight (198) souls on board would perish as a result. The flight engineer and one of the
stewardesses were the only crew members to perish. (National Aircraft Accident Report, 1979)
Flight Crew Experience and Credentials
The person in charge of United Flight 173 that day was Captain Malburn A. McBroom.
He was fifty-two (52) years old and began his employment with United Airline, Inc., on May 1,
1951. He was upgraded to captain on July 1, 1959. Captain McBroom logged twenty-seven
thousand six hundred and thirty-eight (27,638) total flight hours. Of which five thousand five
hundred and seventeen (5,517) were as a captain in the Douglas DC-8. In the previous ninety
(90) days he recorded two hundred and ten (210) flight hours. He had just under fifteen (15)
hours of free time before reporting for this flight. Captain McBroom held an Airline Transport
Pilot Certificate (No.1006880), issued September 28, 1971. He was type rated on the Douglas
DC-8 and the Boeing 727 airframes. He held a first-class medical examination which he passed
on September 22, 1978, with the limitation that the holder shall possess glasses for near vision
while exercising flight duties. Captain McBroom had satisfactorily passed his last proficiency
check ride on September 1, 1978, and his last in route check ride on October 5. 1978.
First Officer Rodrick D. Beebe was forty-five (45) years old and employed by United
Airline, Inc., on June 19, 1965. He was upgraded to a DC-8 first officer on June 21, 1978. First
Officer Beebe recorded five thousand two hundred and nine (5,209) total flight hours to his
logbook. Two hundred and forty-seven (247) of which were as a first officer on the Douglas DC-
8. He too had just under fifteen (15) hours of free time before reporting for duty. First Officer
Beebe held a Commercial Pilot Certificate (No. l-131046) issued on September 15, 1975. He
held ratings in airplane multiengine land aircraft with instrument privileges. He also holds a
rotorcraft rating. His first-class medical examination was passed on October 3, 1978, without any
limitations. First Officer Beebe had his last emergency training on June 24, 1978. He passed his
last proficiency check ride on June 21, 1978, and his Douglas DC-8 proficiency check ride on
August 1, 1978.
Serving as the Flight Engineer, Second Officer Forrest E. Mendenhall was forty-one (41)
years of age. He was employed by United Air Lines, Inc., on December 18, 1967. He was then
upgraded to a DC-8 second officer on January 31, 1975. Second Officer Mendenhall had three
thousand eight hundred and thirty-five (3,895) total flight hours in his logbook as a second
officer. Two thousand two hundred and sixty-three (2,263) of those hours were in DC-8 aircraft.
Just like the other two flight deck crew members he had enjoyed just under fifteen (15) hours
down time before making this flight. hours of free time before reporting for this flight. Second
Officer Mendenhall held Flight Engineer Certificate (No.1819179) issued on February 14, 1968,
with a turbojet rating. He also held the Commercial Pilot Certificate (No.1632855) issued on
April 22, 1965.
He was rated in multi- and single- engine aircraft. engine land and sea with instrument
privileges. His first-class medical examination was passed, with no limitations. Second Officer
Mendenhall had his last emergency training on August 16, 1978. He passed his last proficiency
check February 24, 1978, and his in-route proficiency check December 14, 1978.
The five (5) stewardesses on that flight were all properly trained and certificated in
normal and emergency operations prior to Flight 173’s departure. (National Aircraft Accident
Report, 1979)
Maintenance and Mechanical Issues Contributing Factors
The model of aircraft that United Airlines Flight 173 was operating on this flight was
manufactured by the Douglas Aircraft corporation. The type was listed as the DC-8. The DC-8
first flew in 1958 and was produced until 1972 with five hundred and fifty-six (556) total
variants manufactured. At that time, this was a sleek and modern airliner that was highly capable
and very fast. It could carry two hundred and fifty-nine passengers and was considered an
engineering marvel for its time. (Thomas, 2020)
Aircraft N8082U, a McDonnell Douglas DC-8-61, serial No. 45972, was owned and
operated by United Airline, Inc. It was manufactured May 22, 1968, and is the exact aircraft
operated by Flight 173. The problem that created the confusion on the flight desk with the
uncertainty of the landing gear being locked in the down position is best described by the
following passage of the service bulletin issued for DC-8 found within the N.T.S.B. report.
“On March 27, 1968, McDonnell-Douglas issued Service Bulletin No.32-131, DC-8 SC
1681, Landing Gear Extension and Retraction –Replace Main Landing Gear Retract Rod
Assemblies. This bulletin provided information on the replacement of the retract cylinder rod end
assemblies with machined threads with rod end assemblies with rolled-type threads. In 1973,
United Airlines instituted a gamma ray inspection program for the main landing gear retract
actuating cylinder and rod ends on the DC-8 aircraft. The purpose of inspection was to detect
thread corrosion in the cylinder. The cylinder threads on the main landing gear retract actuators
of the accident aircraft were last inspected using the gamma ray inspection on April 2, 1977. To
provide additional threads and a longer eyebolt on actuator cylinders found with corrosion
damage, the retract cylinder was to have been modified as provided for in the United Airlines
Maintenance Manual dated January 2, 197-I. The right main landing gear retract actuator on the
accident aircraft had not been modified”. (National Aircraft Accident Report, 1979)
The above excerpt clearly shows the failure of the maintenance crews in not correcting
this defective part which became the catalyst for the chain of events that led to the crash of
United Flight 173. It was this corrosion that caused the electrical short circuit that caused the
illumination of the cockpit lighting that gave the crew confirmation of the landing gear being
locked and secured properly for landing. This next excerpt sheds light on how the confusion
began.
“The first problem which faced the captain of Flight 173 was the unsafe landing gear
indication during the initial approach to Portland international Airport. This unsafe indication
followed a loud thump, an abnormal vibration, and an abnormal aircraft yaw as the landing gear
was locked. The Safety Board’s investigation revealed that the landing gears malfunction was
caused by the corrosion in the mating thread where the right main landing gear retract cylinder
assembly was connected to the rod end. The corrosion allowed the two parts to pull apart and the
right main landing gear to fall free when the flight crew lowered the landing gear. This rapid fall
disabled the microswitch for the right main landing gear which completes an electrical circuit to
the gear position lamp indicators in the cockpit.” (National Aircraft Accident Report, 1979)
This confusion is attributed to the loss of situational awareness by the captain and crew
that led to the extensive delay in landing that caused the aircraft to run out of fuel before making
the assigned runway.
Probable Cause Determination and Lessons Learned
Even though the landing gear malfunction caused a chain of events which culminated in
causing the accident, United Airlines had in place procedures for dealing with landing gear
system failures on the DC-8 aircraft and were more than adequate to facilitate the safest possible
operation and landing of the aircraft. Training procedures which included ground school training,
flight training, and proficiency and recurrent training, instruct the flight crew to revert to the
Irregular Procedures section of the DC-8 Flight Manual, which, as stated previously, must be in
the possession of the crew anytime while on flight duty. The irregular procedures section
instructed the crew to determine the position of both the main and nose landing gear using the
visual indicators located on the outside of the aircraft.
The section on irregular procedures clearly states that “If the visual indicators indicate
the gear is down, then a landing can be made at the captain’s discretion.” The flight engineer’s
check of the visual indicators for both main landing gears showed that they were indeed down
and locked, which should have been acceptable to all involved, that a safe landing could be
carried out under precaution. A visual check of the nose landing gear could not be made.
However, unlike the main landing gear cockpit indicators, the cockpit indicator for the nose gear
gave the proper “green gear down” indication. (National Aircraft Accident Report, 1979)
As a result of the information listed above the sequence of events that followed provided
valuable lessons for the future of aviation safety through the adoption of Cockpit Resource
Management that would later be termed Crew Resource Management. It is vital for all crew
members to maintain professionalism and for them to speak up when something is not being
administered correctly. It should be noted that even though the captain is the one who is
ultimately responsible in this situation the other two crew members were also guilty of not
properly monitoring the situation in a timely manner.
There is no excuse for fuel starvation to occur at any time. This holds true whether
someone is driving an automobile, a go-cart, or an airliner. What is most shocking is the fact the
there was a combined experience of thirty-six thousand seven hundred and forty-two (36.742)
hours of flight time. With all the experience located on the flight deck that day it just goes to
show others that anyone can make a mistake. This is why Crew Resource Management is so
important today. Aviation Safety is vital to the life of industry. We must approach each flight
with the utmost of humility and sense of duty. Duty not only to the innocent around us but to our
families as well.
There really isn't anything more that could be added or highlighted that the N.T.S.B.
hasn't already done. They did a phenomenal job in carrying out their assigned duty leaving no
stone unturned. It is rare in these types of accidents where most of the flight crew live to be
interviewed after the fact which provided even greater insight into the chain of events that led to
this tragic accident.
This accident should never have happened. It is easy to speculate being on the outside
and looking in, but we must remind ourselves that a chain of events can lead to catastrophe if the
proper procedures are not adhered to. As Christian aviators we must hold ourselves to higher
standard with the utmost humility in everything we do.
References
MCA. (n.d.). The Stapleton Story | Stapleton MCA. www.mca80238.com.
https://www.mca80238.com/the-stapleton-story
National Aircraft Accident Report. (1979).
https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR7907.pdf
NTSB. (2017). History of The National Transportation Safety Board.
ntsb.gov. https://www.ntsb.gov/about/history/Pages/default.aspx
Thomas, G. (2020, May 26). History of the magnificent DC-8. Airline
Ratings. https://www.airlineratings.com/news/history-of-the-magnificent-dc-8/
