Last Flight of the Unintended UAV


Staff member
Hot takeoffs often lead to cold statistics...

24 June 1971
Yuma International Airport/MCAS Yuma (KYUM/KNYL)
Yuma, Arizona

Cessna 150, N50723
1 Minor

In my time in aviation, I've seen many people learn things, and I've learned many things myself. I see many people that learn things the easy way, however there are always those few that learn things the hard way. I myself have learned things in both ways, in varying situations. Where I am today in aviation is the collective result of all the goods and bads, the highs and lows, and the things learned the easy way as well as the hard way. Probably some of the best learning comes from errors made, whether in the cockpit or not, whether inflight or not. When you commit an error, one that is hopefully not a very bad one, and have the time to go back and review what went right, what went wrong, and what needs to be improved; this is where the real learning occurs. Normally, many of these errors that we've survived become "imprinted" on the brain, and definately not forgotten, since the object lesson they yield is generally of big significance. As I said before, errors come in all shapes and sizes. For todays accident discussion, the learning that came out of this mishap will be one of those errors that remains imprinted for a long time, in my opinion, since though the initial error itself was relatively small; the "balloon effect" it had publically, monetarily, and the fact it resulted in a destroyed aircraft, makes it one of big significance. This accident shows that even the smallest of actions, inactions, errors of commission or omission, in aviation, can have huge outcomes. The good news of the aftermath of this accident is that only one person, the pilot that started the chain of events, received only minor injuries. Lucky indeed, since the event itself contained lots of potential for many more and severe injuries.

The afternoon of 24 June 1971 started as any other day at Yuma International Airport. Marine Corps Air Station Yuma/Yuma International Airport is a joint-use field (ICAO: KNYL/KYUM). It's operations are primarily military, containing at that time, USMC A-4 Skyhawk fleet operations and F-4 Phantom II training operations, as well as US Navy OV-10 training operations and station-based UH-1 helicopter operations for local search and rescue (SAR). Where the east side of the field is military, the west and north side of the field is general aviation, with FBOs on each side as well as a small terminal on the north side and a flight testing facility on the southwest side for McDonnell-Douglas airliner ops. The field has 4 runways, two primary jet/military runways of 13,300 and 9,200 feet length, as well as two primarily civilian runways of 5700 and 6100 feet in length.

On this sunny June day, an 18 year old student pilot with 23 TT, all in the Cessna 150, finished planning a solo out and back flight from Yuma to Calexico, California, where he planned to spend one hour of ground time, get lunch, and return; a 2 hour total cross-country. About halfway through training for his Private Pilot License, he was in the middle of his cross-country timebuilding necessary to meet FAA minimums. Preplanning, checkout, and preflight of N50723 was uneventful. The pilot dutifully followed all applicable checklist items for pre-start; though on start itself, the C-150 would not turn over. Unfortunately, the battery was near dead from the aircraft having sat for the past week and not flown. The student pilot, wishing to get on his way, decides to start the aircraft by spinning the propeller by hand, commonly known as "hand-propping" the aircraft, in order to provide the engine turn-over that the weak battery couldn't via the starter. The student selected the master battery-ON, magneto switch to BOTH, and mixture-RICH in the cockpit, and left a wood chock in front of the left main wheel to hold the aircraft in-place after starting so it wouldn't move. However, the throttle, for some reason, was kept about 3/4 forward to the firewall. The student proceeded to the front of the 150, grabbed hold of the propeller, and gave it one spin in the proper operating direction. The C-150s engine caught the first time and proceeded to accelerate to what some witnesses described as "sounded like over 2000 RPMs." The student, taken aback, jumped out of the way and attempted to run around the left side of the aircraft and get to the cockpit. Unfortunately, at the power setting the 150 was at, it easily jumped the chocks, and began accelerating away down the ramp. The student was unable to get to the cockpit, nor chase down the aircraft as it happily pulled away towards the runways. The C-150 left the ramp, speeding across the taxiway and into the infield, heading for the runways. Just prior to reaching runway 8-26, the C-150 got airborne and headed for the Marine Corps ramp in a slight left turn, and climbing in a shallow climb.

In the MCAS Yuma ATC tower, the local controllers were only working a couple of civilian aircraft since military flight ops for the morning go's had already recovered, and the evening go's weren't scheduled to become airborne for another 5 hours. The junior controller, a Marine E-3, saw the C-150 begin making it's journey from the FBO ramp towards the taxiway, and thought it was taxiing a little faster than usual, not to mention not having called ground control for clearance to enter an active taxiway. The Marine working ground control saw the same thing and immediately made a call on ground frequency asking the taxiing Cessna to relay it's intentions. Both controllers watched incredulously as the Cessna crossed the taxiway, sped into the grass and became airborne, heading for the military ramp. The aircraft made a left banking climb and began a wide circle heading towards the town of Yuma, located (at that time) mostly to the immediate northwest of the base. Still not realizing that the Cessna was lacking a pilot onboard, the tower controller made repeated calls to the aircraft asking it's intentions, informing the non-existant pilot that he had committed numerous flight deviations, ordering him to land immediately, and instructing him to copy down a landline number to call once he landed.

Meanwhile, on the civilian ramp, the student pilot and the eyewitnesses to the hand-propping ran into the FBO to call the Marine Corps tower and report the situation. It took a few tries to convince the tower what had really happened, and what they were now facing.....a pilotless aircraft circling the town of Yuma, Arizona. A hazard to air navigation if there ever was one, not to mention to persons on the ground. Luckily for the Marines, one of their UH-1E Huey air station SAR birds was about 5 miles away returning from a sortie. The tower immediately got in contact with the helo crew, relayed the information to them, and instructed them to follow the Cessna. The helo crew spotted the wayward Cessna in it's lazy left-hand orbit over the city, and proceeded to form up on it, falling into a loose route formation on the outside of it's turn. Meanwhile, at the operations center of the MCAS, the FAA representatives and the senior Marine officers were conferring with local Yuma police and Yuma County Sheriff authorties on how to solve this highly unusual incident. The only viable decisions to be had were to follow the aircraft and see what it does, or take action to bring the aircraft down. The action of shooting down a civilian aircraft over the continental United States was an unprecedented move, a decision that has never before had to have been made. Either way, what goes up must come down, and the biggest problem was where the plane would come down, whether by itself or after having been forced down. One of the problems would be where on the ground needed to be evacuated? In this case, nearly the whole town would have to be evac'd since no one knew where the plane was going. For now, the decisions were still being hashed out among the civilian and military leadership present. By this time, about 1 hour into the event, the Cessna was still circling around Yuma, in a slight climb and now up to about 9,000 MSL. The UH-1E helicopter following the Cessna had advised that it only had about 20 minutes of flight time left due to fuel, and would need relief very soon. Not wanting to leave the Cessna "unattended" in the air, the Marines looked for more aircraft to send airborne. Since MCAS Yuma didn't have an "alert" mission, or aircraft ready to launch at minutes notice, it didn't have immediate jet aircraft ready to launch with crews, since the flying was between go's. In any event it was determined that it wasn't viable to send high speed jet fighter aircraft after the Cessna, which was circling at about 70 knots, since the dissimilar speeds of the respective aircraft were too incompatible.

Luckily for the military, one of the training activities going on at the time was the US Navy OV-10 Bronco squadron, Light Attack Squadron 4. They had been flying the first go, and still had aircraft armed on the ramp in the live load area, as well as pilots available to fly. The OV-10, unlike the stations prevelant jet fighter and attack aircraft, is a twin-turboprop light attack aircraft, which can fly at compatible speeds with the errant Cessna. The Marines ordered one of the Navy OV-10s launched and at about 1.5 hours into this developing situation, one of the VAL squadron aircraft got airborne, armed with 4 x 7.62mm machine guns, as well as 7-shot pods of high-explosive air to ground 2.75 inch rockets. The OV-10 pilot easily spotted the Cessna and took up a trail formation, awaiting further orders as to what to do. After much discussion by the civil and military authorities still as to what to exactly do with this aircraft, there was still an impasse of let the Cessna determine it's own fate, or determine the fate for it. The impasse was solved for everyone after about 2.5 hours into the situation. The OV-10 pilot advised that the Cessna began a shallow descent and seemed to be slowing, having finally run out of fuel. It began descending in a wider and wider bank turn, which by this time, had shifted to the west of Yuma and just across the Arizona/California border. In the early afternoon of 24 June, the inglorious end of the flight of freedom for N50723 came to be. The Cessna descended into a sand dune away from the town of Yuma and was destroyed by ground impact, a little over 2 and a half hours after one of the strangest events in civil aviation began.

Probable Cause:
*Pilot In Command- Engine start without proper equipment/assistance.

Secondary Factors:


Tertiary Factors:


MikeD says:

This accident has all the elements of error chain built in, all in one complete package. Low-time/low-experience pilot, leaning forward a little too much to accomplish the mission, and not using good common sense when faced with a relatively benign situation, that of a nearly dead battery for engine start. One good discussion to have is the concept of hand-propping, the very last event in this error chain that, had it been broken, could have likely prevented this event entirely. Hand propping of airplanes is one of those evolutions that can be performed, heck it's been the way to start aircraft for a long time, and some older/antique aircraft are still started that way. But a few questions have to be answered prior to performing this action, which has the potential to be very safe or very dangerous, depending. 1. Is hand-propping reasonable and prudent?; and 2. Are you properly trained to undertake the action of hand-propping an aircraft?

1. Is hand-propping reasonable and prudent?

Like I stated before, the concept of starting planes by hand-propping has been done since the beginning of flight, and many antique aircraft still use this technique today. Nearly any piston-engine aircraft can be safely hand-propped to start the engine, in the event the normal battery starting is unavailable. But is it reasonable and prudent? I say, it depends. In any normal circumstance, hand-propping is generally unnecessary and in most cases not reasonable nor prudent. If you have an airplane at an airport or an FBO that can not start by normal means, the best and most prudent course of action is to get the problem fixed. Why risk getting injured or having some other problem from this maneuver, when something probably simple can be fixed and the airplane started normally? One of the only times I can think of that hand-propping would be reasonable and prudent in an aircraft that doesn't normally require it would be in some sort of survival situation. That is, you've forced landed somewhere, for some reason repairs/rescue/recovery isn't available, the aircraft won't start normally, and you have multiple people available who are trained and preferably with aircraft/flight experience. Of course this is a very rare situation, but is an illustration of when hand-propping could be necessary, since there's not many "absolutes" in aviation. But I stress the "trained and preferably with aircraft/flight experience" portion of the above, since this leads into the second question that needs to be answered.

2. Are you properly trained to undertake the action of hand-propping an aircraft?

If there's one event in ground operations that literally can mean life or death if not performed correctly, it's the action of hand-propping an aircraft to start. Like I stated before, hand-propping isn't a new concept by any means, but is one of those concepts that if not understood fully, practiced to proficiency, and performed correctly, has the great potential to result in injury or death. One of the biggest mistakes made in those that undertake this endeavor is attempting to perform it solo. In addition to the training necessary, hand-propping is a multi-person event; a multi-trained person event. There have been numerous incidents of pilots having an untrained spouse, friend, or family member "hold the pedals" while they hand-propped the aircraft, often with dire results. The operation requires the trained persons to know what they're doing, or at least know operations of the particular aircraft, have clear communications with other, preferably be able to physically see each other during the operation, and be fully briefed and in agreement with each other on exactly what and how the operation is going to be performed. At a minimum, in my opinion, two trained people are needed to undertake the operation: one performing the hand-propping, and one to be in the cockpit to hold brakes/parking brake etc. Optimally, 3 or more trained persons would be good, so as to have safety observers and communications assistants. Remember, all this is in the unlikely event you'd have to hand-prop an aircraft that doesn't normally require it. Even those that hand-prop aircraft for a living with planes that do require it, cannot get complacent at any time, no matter how many times they've performed it. Every time performing hand-propping contains the same high-risks as the time before.

An Interesting Sidenote

Even though this was 1971, the decision to shoot down civilian aircraft over the continental United States in a necessary situation would still never really be resolved. Between the time of this incident and today, there were a few high-profile incidents of this very quandry in-effect:

On 24 November 1971, exactly 5 months to the day of the Yuma, AZ incident, famed-hijacker D.B. Cooper took control of a Northwest-Orient Boeing 727-100. Following a threat to blow up the plane and a demand of $200,000 and 4 parachutes, Cooper released the passengers at Seattle-Tacoma International Airport, and the aircraft departed Sea-TAC for Mexico, trailed by 2 USAF F-106 Delta Dart fighters from the 318th Fighter Interceptor Squadron (FIS) out of McChord AFB, Washington. The true intent of Cooper was unknown, and there was scenario discussion of what he was truly planning to do with the Northwest jet and it's crew. Though the F-106s were fully armed, their mission was to shadow the airliner, though they could be employed if absolutely needed. As it was, Cooper parachuted with the cash from the aft airstair of the 727 somewhere over Oregon, and remains on the loose to this day.

On the night of 10 January 1980 a Cessna 441 Conquest with one pilot onboard and legendary Louisana State football coach Bo Rein as a passenger, deviated off course during a flight from Shreveport, Louisana to Baton Rouge, a 40 minute flight. With no response to ATC, and climbing east up to altitudes of FL 400, chase aircraft were scrambled to intercept the Cessna. Two Michigan Air National Guard F-4C Phantoms from Seymour-Johnson AFB and two USAF 48th FIS F-106 Delta Dart interceptors from Langley AFB were dispatched to intercept the Cessna. They reported no external damage to the twin Cessna, and only a red glow from the instrument panel, with no crew present in the cockpit. The Conquest eventually ran out of fuel, and descended into the Atlantic Ocean, 100 miles east of Langley, Virginia; both onboard presumably killed.

On 16 December 1988, a Learjet 24B with two crew onboard, including NASA astronaut candidate Susan Reynolds, failed to communicate with ATC shortly after takeoff from Memphis, TN and bypassed it's destination of Addison, TX by 425 miles, eventually crashing near the town of Cuatro Ciengas, Mexico after running out of fuel, killing both onboard. A USAF T-38 from the 560th Flying Training Squadron (FTS) at Randolph AFB, TX sent up to intercept the Learjet, reported frosted-over windscreens, an indication of cockpit depressurization onboard, and no response from the crew, which he also couldn't see.

On the morning of 25 October 1999, 2 crew and four passengers, including famed PGA golfer Payne Stewart, perished in the accident of their Learjet 35, in an incident with striking similiarity to the Rein incident mentioned above. Departing Orlando, Florida for a flight to Dallas, Texas, the Lear eventually crashed in South Dakota after flying on autopilot. USAF and Air National Guard F-16s that intercepted the Lear reported it's windows to be frosted over, similiar to the 1988 Learjet accident. In the Rein, Reynolds, and Stewart cases, there was discussion at the National Command Authority (read...President and Secretary of Defense) level of what to do if either of these planes began to head towards a heavy-population area. Discussion of possible shootdown was in progress.

Of course, the events of 11 September 2001 are well known to anyone in the world, and in specific, the decision made that day to shoot down threat airliners or other civilian aircraft that posed a clear and present danger or whose intentions were otherwise unknown.

As can be seen, numerous, more high-profile events similiar to the 24 June 1971 incident over the city of Yuma, Arizona have overtaken this story. But in addition to the direct factors involving why this mishap occurred, the mishap itself further opened the pandora's box of what to do with civilian aircraft that, for one reason or another, became hazards to air navigation or to persons on the ground. For better or for worse, we have definately come a long way since the Last Flight of the Unintended UAV.


The above is not intended to be an undue criticism of the person or persons involved in the incident described. Instead, the analysis presented is intended to further the cause of flight safety and help to reduce accidents and incidents by educating pilots through the sacrifices of others in our profession.
I guess back then they were still teaching to trim the aircraft prior to start for the appropriate cross-taxiway-cross-grass-cross-runway rotation and sightseeing tour setting.
They needed one of these bad boys:


Throw some ropes around the wings and shoot the engine with some of your machine guns. That was the first thing that popped into my head when reading this. It was close enough to Texas, must have been a few cowboys around to rope in a 150.