The owner of this Model S says he would buy another one of the battery cars despite the fire.

The Tennessee doctor whose Tesla caught fire last week is defending the maker and insists he will buy another one of the electric vehicles – even though the third fire involving a Model S in barely six weeks has triggered a preliminary federal investigation and a sharp slump in the California maker’s once seemingly unsinkable stock.

The latest fire resulted from an incident that occurred in Smyrna, Tennessee – ironically, the same town where Nissan produces its Leaf battery-car.  According to a statement released by owner Juris Shibayama, he was traveling at 70 mph when he struck what appears to have been a vehicle trailer hitch that had come loose on the highway. Moments later, Shibayama received the first in a series of warnings advising him “pull over safely.” He exited the vehicle as smoke began to pour out of the front battery compartment.

“This experience does not in any way make me think that the Tesla Model S is an unsafe car,” the doctor wrote on the Tesla blog page.  “I would buy another one in a heartbeat.”

The owner of the first Tesla Model S to catch fire – also due to damage from road debris in a Seattle suburb in late September – wrote a similarly positive letter to the battery carmaker’s CEO Elon Musk following his incident.

The third fire occurred in Mexico after a motorist slammed into a concrete wall.

Last week’s fire likely couldn’t have come at a worse time for Tesla. After a huge run-up in its stock price – which peaked at $194.50, compared to a 52-week low of just $29.85 – the maker’s shares have been in near-freefall since the beginning of October.  On Friday, they fell another $1.82, or 1.3%, to close at 137.95.

Meanwhile, the National Highway Traffic Safety Administration has announced a preliminary investigation, stating that it “is in close communication with Tesla and local authorities gathering information about the incident to determine if additional action is necessary.”

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Industry analysts have been boisterously debating whether the slide in Tesla stock is just the beginning of a further decline or just a temporary aberration.  Gordon Johnson of Axiom Capital Management told CNBC during an interview late last week that, “I think the stock is grossly overvalued.”  But Wedbush Securities analyst Craig Irwin told the network he thought little would come of the NHTSA investigation and that Tesla would likely regain its momentum.

Curiously, Tesla CEO Musk actually suggested the maker “had no right” to the $200 share price it neared last September. That said, there is little doubt the California start-up is now struggling to maintain that momentum – notably alerting the media to the positive comments by two of the three Model S owners to have experienced fires.

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According to Shibayama, he spotted a rusty trailer hitch on the highway but “did not have enough time to swerve to avoid the hitch, and it went below my car. I felt a firm ‘thud’…and it felt as though it even lifted the car up in the air,” he wrote. “Somewhat shaken, I continued to drive.”

In less than a minute, the doctor received his first warning that the car would need service and might not start. He was then advised to pull over “safely,” as the car was about to shut down.

“I got out of the car, and started to get all my belongings out,” Shibayama recalled. “About 5-10 seconds after getting out of the car, smoke started to come from the front underbody of the car. I walked away from the vehicle to a distance of about 100 yards. More smoke started to come out of the bottom of the car, and about two minutes after I walked away, the front of the car caught on fire.”

The fire trucks arrived quickly and soon has the fire extinguished. According to the doctor, the flames never reached the passenger compartment. The blaze was similarly limited to the front battery bay in the first reported Model S fire.

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NHTSA has given no indication of how long it will take to complete its preliminary investigation. The results could trigger a larger examination – or possibly a recall – though the safety agency could also decide that the Model S design actually proved safe under the circumstances.

The more immediate question is whether the ongoing headlines will hurt Tesla’s sales. The maker has, if anything, been struggling to meet strong demand in recent months and actually warned analysts, during a phone call following the release of third-quarter earnings last week, that it was running short of batteries and unable to keep up with demand.

Tesla this month inked a deal with Panasonic to expand battery production. It remains to be seen if it will need more batteries.