Ukraine's smart air defense threatens one of Russia's most advanced jets, leaving it too scared to use them, experts say

• Since the start of the war, Russia's air force has struggled in combat over Ukraine.
• It has been particularly careful with using its advanced Su-57s over Ukraine, UK intel recently observed.

Ukraine's air defense is a threat to one of Russia's best aircrafts, leaving its commanders too scared to deploy them, experts told Insider.

Since the early weeks of the war, Russia has surprisingly failed to secure air dominance over Ukraine, despite having an advantage in both numbers and technology.

In particular, Russia has boasted about its fleet of Sukhoi Su-57s, its most advanced supersonic combat jet to date.

But, per an intelligence update earlier this week from the British ministry of defense, Russia has only used the jets from within its own airspace.

One expert told Insider that part of the reason for Russia's reluctance is Russia's successful air-defense strategy.

The expert, Justin Bronk, is an airpower expert with the Royal United Services Institute (RUSI) think tank in London.

"The Ukrainians have so far been so successful in defending their airspace because the Russians haven't been able to reliably locate and destroy Ukrainian mobile missile systems," Bronk told Insider.

Meanwhile, the "Russians are not comfortable and not confident" in their jets' ability to evade those defenses.

The shape of the Su-57 is meant to help it avoid radar, making its footprint far smaller than older Russian jets. But, Bronk said, Russia seems not to want to rely on that.

Dr. Matthew Ford, a professor at the Swedish Defence University, also credited Ukraine's air defense to deterring Russian incursions.

"The fact that they're not committing [Su-57s] in battle tells you ... that Ukrainian air defenses are more sophisticated and are able to take out Russian aircrafts," Ford told Insider.

"[Ukraine's] air defense is sufficiently credible to make it open to question for the Russians as to whether they want to commit their air power," he added.

Another reason why Russia might not be using the Su-57 in battle is that it doesn't actually have many of them, Bronk said.

It is unclear exactly how many Su-57s Russia has. However, the British defense ministry cited a satellite image taken on December 25 indicating that five jets were housed at the only known Su-57 air base in Russia.

"They're being very cautious with their entire combat aircraft fleet, and despite that, they continue to take a steady trickle of losses," Bronk added.

The General Staff of the Armed Forces of Ukraine said in an update on Thursday that Russia had lost more than 280 planes since the beginning of its full-scale invasion of Ukraine.