The ubiquitous Soviet-era passenger jet remains the chief workhorse of airlines throughout the former USSR.
Almost 40 of the machines (out of some 1,000 produced) have been lost in fatal accidents since it was introduced in the early 1970's, a record that Russian experts insist is equal to that of comparable Western aircraft, such as the Boeing 727 and 737.
Four crashes in Iran
But four of those Tu-154 accidents - a disproportionate 10 percent of them - have occurred in Iran over the past 16 years, killing almost 450 people and leading some experts to scratch their heads for an explanation.
"They have a long experience with the Tu-154 in Iran," says Oleg Panteleyev, editor of the Russian-language online aviation newspaper Aviaport.ru. "They have dozens of these aircraft in service, along with lots of highly qualified specialists and local servicing centers."
Though Iran has trouble purchasing new airliners due to international sanctions, Mr. Panteleyev says there is no difficulty in obtaining spare parts for the old Tupolev planes, which are not subject to any restrictions.
Three of the Iranian accidents have occurred with planes flown by Iran Air Tours, a mainly domestic charter operator that lists ten Tu-154's in its inventory.
In 1993, one of the airline's Tu-154's collided with an Iranian airforce Sukhoi fighter jet, killing all 132 aboard. In 2002, another crashed into an Iranian mountainside in adverse weather conditions, with 118 fatalities. And three years ago, another of its Tu-154's burst into flames after landing at Mashad airport, killing 28 passengers.
Wednesday's accident involved a Tu-154M - the plane's latest variant - belonging to Caspian Airlines, a joint Russian-Iranian company, that was en route to the Armenian capital of Yerevan. The flight crashed shortly after takeoff, according to the Fars news agency. Witnesses told the Iranian news agency the plane was on fire when it hit the ground.
Experts say it's too soon to pinpoint the cause of that crash.
No blacklisted aircraft
Last month, the crash of a Yemenia Airways Airbus jet prompted questions of a double-standard because the 19-year old aircraft was blacklisted from French airspace due to unspecified safety "deficiencies" discovered by inspectors.
Yesterday, the European Union released its annual aviation blacklist of some 200 commercial airlines. They are forbidden to land in Europe because of safety deficiencies. Neither Iran Air Tours or Caspian Airlines were on the list.
Russian experts argue that the diverse causes of past accidents in Iran fits a larger pattern of Tu-154 crashes, which they say tend to come down to pilot error, poor maintenance, or just plain freak occurrences.
In the past few years, several Tu-154's flown by post-Soviet airlines have gone down due to a tragic bouquet of unique reasons, including terrorist attack, a bizarre air traffic mistake that led to mid-air collision over Germany, and an accidental shootdown by Ukrainian air defenses.
These are old aircraft
"The Tu-154 has been in service a long time, and is considered to be a really safe plane," says Roman Gusarov, editor of Avia.ru, an industry information service.
"Of course it's old, and it doesn't meet modern requirements for noise pollution, fuel consumption, and ecological standards," which bars it from flying to most Western destinations nowadays. "But still about half of the commercial passenger planes in use in Russia are Tu-154's, and they'll probably be in use for quite awhile to come".
It might just come down to age. Most of the Tu-154's that remain in service in the former USSR, and in dozens of airlines of developing countries around the world such as Iran, were produced in Soviet times.
"The majority of these planes are 30 to 40 years old, and are working at the limits of their potential," says Mr. Gusarov. "Everything has a lifespan."