More than a year ago, the U.N. dropped the Russian air transport company Vertikal-T from its approved list of vendors after a fatal helicopter crash in Nepal.

Yet NATO continued to use helicopters owned by Vertikal-T in Afghanistan. And on July 19, one of those choppers crashed at southern Afghanistan's largest NATO base, killing 16 civilians on board.

The crash reflects a little-known reality behind NATO's military push in Afghanistan: It is relying on Russian aviators flying Soviet-design aircraft, who are clocking up lucrative contracts in a country Russian troops left two decades ago.

Aviation industry analysts say many of these contractors have bad safety records, and allege that NATO has hired some operators with questionable backgrounds through arms-length leasing deals. These same analysts say governments have outsourced crucial military contracts to little-known companies.

"Normally this would be handled by the military, but the military have been cut back. ... They are plugging the gaps with dodgy operators," said Hugh Griffiths, an analyst at the Stockholm International Peace Research Institute, or SIPRI.

Spokesman Ari Gaitanis wrote in an email to The Associated Press that the U.N. suspended and removed Vertikal-T from its list of approved companies because of "serious violation of international safety requirements."

But the company responded to the AP that it was dropped because "Vertikal-T could not sufficiently prove that it could comply with the requirements and regulations of the U.N." It added: "There is no mention of safety." Vertikal-T also noted that it is subject to Russian air safety regulators, and recently had its Russian commercial license renewed as an air carrier.

Russian companies play a big role in providing non-combat air support in NATO's war against the Taliban. In Russia, where the NATO alliance — set up to counter the Red Army — is still viewed as a threat, Russia's involvement in Afghanistan is seldom discussed.

In 1989, the Soviet Union limped away from a ten-year war in Afghanistan that cost 15,000 Soviet lives and hastened the end of the empire. Moscow then armed both sides of a vicious war that pitted Afghan factions against one another. When the U.S. went to war with Afghanistan in the wake of Sept. 11, the Russians continued to play a clandestine supporting role.

Now, the Russians are back in Afghanistan in force.

"We never left," said Pavel Felgenhauer, a Moscow-based military analyst. "Officially, Russia is not involved. Unofficially, it is."

Faced with a shortage of helicopters, NATO countries are turning to cheap Eastern European and particularly Russian operators to ferry supplies and civilian contractors, as well as recover downed choppers. The modified Russian planes are ideally suited to the dust, heat and high altitudes of Afghanistan, and their pilots are used to punishing conditions.

Western analysts say they are also prepared to take risks. Russia's aviation sector has a spotty safety record, they point out, with helicopters crashing on a frequent basis. Poor maintenance is often cited as the cause.

Intermediaries such as Toronto-based Skylink Aviation often handle the actual subleasing for NATO forces, giving governments an element of "plausible deniability," these experts say. The Fluor Corporation, a Texas-based company providing logistical back-up to U.S. military operations, said Skylink provided the Vertikal-T helicopter that most recently crashed in Afghanistan. The helicopter was transporting contractors on behalf of Fluor.

Vertikal-T's reputation is as the "hot zone provider of choice," said Mark Galeotti, a military and organized crime expert at New York University. "If you want a pretty professional but slightly cowboyish outfit that doesn't mind flying into war zones, doesn't mind taking off from unsurfaced runways, then Vertikal-T now seems to be the front runner," he said.

Experts say these companies generally provide legitimate air transport services. But too often they draw the wrong kind of publicity.

Vertikal-T, based in the city of Tver northwest of Moscow, was left red-faced in Sudan after authorities accused it of dropping arms to rebels, an allegation the chopper company strenuously denied.

Volga-Dnepr was also dropped from the U.N.'s vendor list in 2007 after it allegedly paid bribes to a U.N. employee to secure multimillion dollar contracts. The company did not respond to requests for comment on this issue.

And Aviacon Cargo, a Urals-based company that flies lighter Ilyushin planes into Afghanistan, was singled out in a SIPRI report after the UN noted suspicious movements in Tanzania. SIPRI claimed Aviacon shipped arms on behalf of Russian defense companies to equip antagonists in African conflicts. Aviacon insisted, however, it has never been involved in illicit flows of arms.

NATO's logistics arm, NAMSA, said it did not have any direct contracts with Russian companies, but admitted it did not probe its subcontractors.

A NATO spokesman declined to provide information on individual companies, but said it was "important to bear in mind the great demands placed on our countries' forces. ... Missions carried out by the individual nations, the United Nations and the European Union involve calling on nations' assets, both manpower and equipment."

NATO uses Russian aircraft in two main ways. At one end of the scale, Russian choppers take on simple supply missions. At the other end, massive Russian-owned Antonov planes are taking off from distant air bases, such as RAF Brize Norton, the United Kingdom's largest station, bound for the deserts of Afghanistan with heavy and sometimes classified freight.

While the air service companies are private corporations, experts say they almost certainly operate with Kremlin oversight.

"At the very least, there is an acquiescence," said Galeotti, a military and organized crime expert at New York University.

Indeed, there appears to be a quid pro quo. Just days after Russia agreed to allow the U.S. to transship lethal Afghanistan-bound cargo via Russian territory, Russian cargo company Volga-Dnepr — which already has contracts with the U.S. military — said it was in the lead running for a U.S. tender to fly supplies to Afghanistan.

RIA-Novosti news agency quoted chief executive Valery Gabriel as saying Washington had been advised to choose a Russian carrier for this critical service.

For the Kremlin, Russian carriers mean a degree of control over these shipments. Russian Foreign Minister Sergey Lavrov said Russia reserves the right to inspect all cargo flown across its territories.

For the carriers, the work means millions in revenue. The U.S. Transport Command said it has awarded Volga-Dnepr and another Russian company, Polet, $400 million in contracts up to September 2009 in the past year.

Figures for chopper companies are harder to obtain. All of the companies approached refused to divulge both numbers and the identity of their government clients, citing confidentiality.

"Russia is delighted to be involved," said Galeotti. "One, it's big business. Secondly, they are very keen for allied forces to be increasingly dependent on supply lines through Russia."

He added that Russia's GRU, its military intelligence arm — believed to have close links with several Russian companies operating in Afghanistan — may also stand to benefit.

"From a GRU standpoint, you have an extremely useful source — low-level but extremely useful intelligence," he said.