The Russian air force grounded its entire fleet of Sukhoi Su-27 fighter jets on Thursday after a fatal crash near Moscow. The Su-27, commonly known as Flanker — the code name given to it by NATO, which assigns one to every piece of Russian military hardware — is the backbone of Russia's air force. The grounding means that about half of Russia's fighter jets cannot take to the air.

According to Reuters, aviation sources told Russian agencies the crash looked like the result of an unspecified technical failure.

General Viktor Bondarev, the head of the air force, ordered the country's fleet of the twin-engined fighter jet grounded until the reasons for the crash had been determined, Russian agencies reported.

Thursday's crash occurred just outside Moscow and involved an Su-27 that was part of the air force's aerobatic demonstration team, the Russian Knights, who have overflown annual Red Square military parades in the past.

Two Sukhoi Su-27 jet fighters of the Russkiye Vityazi (Russian Knights) aerobatic team perform over Alabino outside Moscow, Russia, 1 August 2015. Photo by Maxim Shipenkov/EPA

The Russian Defence Ministry was quoted as saying that the pilot of the downed plane, who was killed, did not have time to eject because he had used his last seconds to steer the aircraft away from a populated area.

The plane was returning to its base at the time and, as is normal for fighters used as aerobatic demonstrators, was not carrying weapons or ammunition, the ministry was cited as saying.

Russia has 321 Flankers of various models in service, according to Flightgobal's World Air Forces 2016 yearbook. The rest of its fighter jet force is made up of smaller, short-range, widely exported Mig-29 Fulcrums and a small contingent of Mig-31 Foxhounds, big and extremely fast interceptors designed to defend the vast expanse of Russia's Far East.

Russia has the world's second-biggest air force after the United States. That is one of the major legacies of the Soviet Union, which left the Russian Federation with world-class airpower. But most of Russia's warplanes, including the Flanker, are aging if capable Soviet-era designs, and aren't maintained to the same exacting standards as the West's.

Yet the Flanker, especially in its later variants, remains a fearsome airplane.

Blessed with spectacular agility despite its large size, the Flanker stunned the West with unprecedented aerobatics when it appeared at the Paris Air Show in 1988, back when the country building it was still the Soviet Union. Bigger than the American F-15 Eagle fighter it was designed to match, and weighing at takeoff as much as a 70-seat airliner, it can carry a large amount of weapons and fuel and sports a large radar, enabling it to see opponents at very long distances.

The Su-27 has spawned several derivatives, all called Flanker too, which largely look like the original.

Four of those derivatives — the Su-27SM3, Su-30 and Su-35 air defense fighters and Su-34 bomber — are fighting in Syria as part of the Russian contingent there. It isn't clear whether the grounding order affects them as well.

The Su-34 or Fullback is bigger, sports a very different front section, and is capable of precision bombing with laser- or optically-guided munitions. Yet footage from Syria often shows it employing "dumb," free-fall bombs, which are cheaper but pose a much higher risk of hitting civilians.

In Syria, the Sukhoi fighters are based with the rest of the Russian planes at Hmeynim airbase near Latakia, in the heart of the area still under control of the Syrian regime. Their role is to use their long-range radar and missiles to cover the skies where the other Russian aircraft operate.

Thanks to Indian Air Force pilots who have been flying an export version of the Su-30 for years and have trained with the US Air Force during major exercises, the Americans have good insight into what the newest Flankers can do.

In fact, the first time they encountered it in an exercise in 2004, the Flanker positively clobbered them: At the end of the wargame, an average of nine US F-15s had been (virtually) shot down per each Su-30 killed. As the West's air forces learned more about their best potential adversary, the numbers changed, but the Flanker still commands respect from its opponents.

Over Syria, the Russian Flankers and American planes have come close — in some cases as close as 1,500 feet or 500 meters — but, so far, there haven't been any hostile incidents. The two sides have agreed on so-called "deconfliction" procedures, essentially telling each other how to minimize the risk of being in the same place at the same time and what to do if that happens. In 30 years of operation, no Flankers have engaged a Western fighter in combat.

The Thursday crash of a Flanker near Moscow was a rare occurrence, in that it was the third loss in the same week of an aerobatic jet. The US Air Force's Thunderbirds lost an F-16 on Tuesday and the US Navy's Blue Angels an F-18 the same day. The pilot of the Thunderbirds jet ejected safely, but the officer piloting the Navy jet was killed. In an improbable string of events, a fourth crash of an aerobatic jet happened on Thursday shortly after the Su-27 accident: an F-5 Tiger of the Swiss Air Force's Patrouille Suisse went down in the Netherlands after a mid-air collision. The pilot ejected to safety.

Follow Alberto Riva on Twitter: @Albertoriva