Source: APRO Bulletin, Vol. 24 No. 2 (Aug 1975)

On May 2, 1974, Carlos Antonio de los Santos Montiel, 23, left Mexico City in his Piper Aztec 24, registered as XB-XAU, for Zihuatenajo, state of Guerrero. He arrived there in the afternoon and although he had originally planned to return that day, he decided to stay over and return on the 3rd. He had dinner at 8 p.m. and retired.

The morning of the third was cloudy with considerable smog, mist and very poor visibility. Carlos took off, nevertheless, at 10:30, without having his breakfast. He climbed his little plane to 13,500 feet but conditions were still bad so he climbed to 14,500 where he found a clear blue sky and continued on his return trip to Mexico City.

Arriving in the area of Tequesquitengo, Carlos decided to lose altitude in order to make visual contact with Lake Tequesquitengo and verify his position, instead of depending on his instruments. When he got down underneath the cloud cover, ground mist and fog blocked his view of the Lake. Then things began to happen.

When he looked from the left (he had been gazing through his left side window) to the front he became aware of something on his right and glanced in that direction and was shocked to see an object with the appearance of two plates joined together at the rim with a cupola which had what seemed to be a little window and an antenna on top. It was positioned 20 centimeters above the surface of the wing and about 1 1/2 meters from the Piper's cabin. (See drawing by Staff Artist Robert Gonzales.) A glance back to the left revealed another object of the same description in the same position above the left wing.

"I was petrified," Carlos told officials later, "after I saw a third object which seemed about to collide head-on with the windshield. But it went beneath the aircraft and I heard a strange noise from below as though it had collided with the underside of the plane."

Carlos then noted that his airspeed had decreased from 140 nautical miles per hour to 120. He tried to bank to the left, in an attempt to "bump" the object away from his plane but the controls were frozen and would not move. He then tried to let down the landing gear, hoping to get rid of the object under him, but with no results.

APRO's Field Investigator, Fernando J. Tellez Pareja, listened to the tape-recorded conversation between Santos and the Mexico City International Airport Control Tower, which Carlos initiated after he found his controls were frozen:

Carlos: Center Mexico from extra bravo extra alfa union. Mayday! Mayday! (Ed. Note: "Mayday!" is an international distress signal.)

Mexico City: Come in, extra bravo extra alfa union. (Here the pilot repeated his call twice — apparently he did not hear Mexico City answer.) Center Mexico here, come in extra alfa union.

Carlos: Extra alfa union to Center Mexico. My aircraft is out of control — I have no control over it — I have three unidentified objects flying around me. I have three unidentified objects flying around me, one came under my aircraft and hit it. The landing gear is locked in and the controls won't release them. My position — I am on the Radial 004 from the VOR Tequesquitengo — I am not controlling the plane — Center Mexico, can you hear me?

Center Mexico: Take note extra alfa union, give me your position and your situation. We are contacting competent authorities and (here interrupted by Carlos again)

Carlos: The aircraft is out of control.

At this point, Mexico City International Airport closed its runways to traffic and prepared for the expected emergency landing. The objects continued maintaining position on XB-XAU, exerting complete control over the aircraft.

The "Mayday" or emergency call was received at 12:15 p.m. on Saturday, May 3. The control tower contacted Ignacio Silva la Mora (Carlo's uncle), an authority on aircraft, who was put in touch with Carlos via radio to analyze the problem and help with landing preparations.

When Carlos had reached the Ajusco navigational fix, the UFOs had elevated the aircraft from 15,000 feet (the altitude while over Tequesquitengo) to 15,800 and then, one by one, they left. First the object over his left wing elevated until it was over the cabin, then above the object on the right wing, and then these two flew off and were lost to view in the direction of the Popocatepetl and Iztaccihuatal volcanoes. The controls of the aircraft were immediately normal and Carlos regained control.

Carlos then attempted to lower the landing gear, circling Mexico City International Airport eight times, in radio contact to ascertain if he was successful. Finally, after 40 minutes of circling while he worked on the control column with a screw driver, he managed to lower the wheels and landed at 1:34 p.m. on the grassy area between runway 5 right and 5 left where emergency vehicles, including firemen and ambulance, were waiting.

After landing, Carlos was taken to the Airport Clinic where he was thoroughly examined and found to be normal and fit. Some individuals had hinted that he might have been under the influence of drugs or alcohol but the medical examination laid that speculation to rest.

Two days after the incident, Captain Augusto Ramirez Altamirano (Chief of Inspectors for the region from the Aeronautical Civil Direction) said that Carlos would have to undergo a series of tests to determine if he had really seen the UFOs or if they were an illusion from flying too high without oxygen.

On May 7, Dr. Luis Amezcua, Chief of the Aviation Medicine Department of Mexico City International Airport, completed a series of medical tests (neurological, physical and psychiatric, etc.) and gave his opinion that Carlos had been suffering from low blood sugar because he had not eaten from 8 p.m. the night before until after the incident the next day and inferred that Carlos had hallucinated.

Field Investigator Telles interviewed the witness and gives us the following insight: Carlos de los Santos is 23, has been a pilot for two years, has 370 flying hours to his credit, has a private and commercial pilot's license. He is employed by Pelletier, S. A., a company which specializes in analysis and study of water. His father is Chief Mechanic of the Mexicana de Aviacion Airlines. Carlos neither smokes nor drinks, is not interested in science fiction and has never read a UFO book.

As far as radar confirmation was concerned, Mr. Julio Cesar Interian Diaz, the Mexico City International Airport Terminal Radar Controller, said that the distance from Tequesquitengo to Mexico City is 48 nautical miles and that the blip of Carlos' plane was picked up on radar when 43 miles out of Mexico City. Carlos' aircraft was the only one in that sector at that time. The radar registered the separation of another blip which went in another direction from Carlos' plane, executing a 270-degree turn in a radius of 3 or 4 miles at a speed of 450-500 nautical miles per hour. Mr. Interian Diaz said that he did not know of any aircraft which could execute such a maneuver.

Further in-depth investigation is being conducted by an aeronautical engineer with the help of Field Investigator Fernando Telles. We should note here that this is Mr. Telles' first important case and he has done an outstanding job of investigating and reporting.

(Editor's Note: Regarding the theorizing concerning the low blood sugar reaction: Carlos exhibits none of the symptoms of hypoglycemia (low blood sugar): sluggishness, irritability, overweight. Had he actually been a diagnosed hypoglycemic and suffered such a fearful hallucination, the fear would have triggered a release of adrenalin into his blood which would have, in turn, triggered a high flow of insulin, resulting in shock, in which case he would not have been able to land the airplane.)