The tracking of planes has become a kind of global sport, as largely amateur photographers post thousands of images showing arrivals and departures in their attempts to chronicle flight paths. In the case of this plane, for example, one spotter spied it leaving an airport in Zurich around the time of the World Economic Forum in Davos, Switzerland, held in January. Another photographer tracked the plane, identified by its call letters N604EP on the tail engines, departing a London-area airport for Ghana last October.

But this week’s spotting by a New York Times reporter in Tehran carries particular intrigue because it involves Iran, a country still effectively shunned by the global financial system.

Even some former federal officials, who spoke on the condition of anonymity, said the very presence of an American-flagged aircraft parked in broad daylight suggested its flight had been approved as part of a legitimate business trip. What is more, they said, the easily identifiable plane was not likely to be part of a covert diplomatic mission.

The secrecy surrounding the plane is compounded by federal aviation regulations that can make it virtually impossible to determine who was flying it.

The private plane, like thousands of similar ones, is owned through a trust — a complex legal structure often established to help foreign individuals or corporations invest in planes that can fly freely within the United States. Aside from that benefit, the structure enables investors and operators to remain largely anonymous to the public. The trustee — in this case, the Bank of Utah — is the sole entity recorded as owner in a vast database maintained by the Federal Aviation Administration.

The Bank of Utah is listed as a trustee for 1,169 aircraft, ranging from Boeing 747s to single-engine Cessnas, according to a review by The New York Times of the database. The Bank of Utah acts as a trustee for more planes than just about any other bank, the review shows.

Mr. King, who helps run the bank’s trust services business, said the bank had no “operational control” or “financial exposure” to any of the planes.