The 1957 Kirtland AFB NM UFO encounter

The 1957 RB47 radar reflecting and IFF electronic signaling UFO case is a classic apparent nuts-and-bolts UFO vehicle encounter and has already been covered in this forum. It turns out that that there were several other high-profile UFO cases that year, that from their descriptions seem to be related. One of them was the 1957 Kirtland AFB NM UFO encounter.  

Background: from NICAP documents, at https://www.nicap.org/chronos/1957fullrep.htm :

A major sighting wave year, 1957 is best-known for the Levelland, Texas sightings which began on Nov. 2. However, the key cases are the IFF electronic signaling and radar-emitting UFO cases such as RB-47 (July 17) and several others within a week or two before and after, the radioactivity case at Montville, Ohio (Nov. 6) and the nuclear weapons storage area case at Kirtland AFB, New Mexico (Nov 4), all cases of supreme scientific value. Prior to the wave flap, the Sept 20, 1957 radar tracking caused a White House and top intelligence alert. A very important year in UFOlogical history. 

More specifically on the Kirtland AFB encounter, from a summary description in NICAP documents, at https://www.nicap.org/kirtland57dir.htm :

CAA tower personnel, R.M. Kaser and E. G. Brink, were reliable observers with 23 years of airport control tower experience between them. A lighted object came down steeply at the east end of a runway, left the flight line, crossed runways, taxiways, and unpaved areas at about a 30 degree angle, and proceeded southwest towards the control tower at an altitude of less than 100 feet. Observed through through 7x binoculars, the object appeared to be egg-shaped, having no wings, tail, or fuselage, and was elongated vertically. It appeared to be fifteen to twenty feet tall, about the size of an automobile standing on its nose, and had a single white light at its base. After the UFO left the area it was tracked on a CPN-18 surveillance radar and it exhibited some amazing flight characteristics. The object also came back towards Kirtland until it took up a position behind an Air Force C-46 that had just taken off. It stayed in position behind the C-46 until they both moved out of radar range.

Like in the RB47 encounter, the data is of high quality with excellent experienced and reliable observers and correctly functioning radar equipment. I would be interested in an explanation that doesn't at least mention the high possibiity that this was a physical vehicle that emitted visible light and reflected radar signals.

Observed through through 7x binoculars, the object appeared to be egg-shaped, having no wings, tail, or fuselage, and was elongated vertically. It appeared to be fifteen to twenty feet tall, about the size of an automobile standing on its nose, and had a single white light at its base.

So it's a giant flying egg? That doesn't by necessity suggest a nuts & bolts vehicle to me, though I do accept the possibility it's a vehicle of sorts.