Here is what we know.
On Feb. 26, 2019 Indian planes crossed the line of control at India's border with Pakistan and bombed what New Dehli described as a terrorist training camp near Balakot.
(This first appeared in March 2019.)
Several days of aerial fighting followed the bombing raid. On Feb. 27, 2019, Pakistani F-16s and other planes crossed the line of control to attack Indian forces, New Delhi claimed.
Indian MiG-21s and other fighters intercepted the Pakistanis and shot down one F-16, killing its pilot, according to the Indian government. Islamabad claimed its forces shot down two MiG-21s, but New Delhi copped to losing just one jet.
Pakistani forces captured the MiG-21 pilot, Wing Commander Abhinandan Varthaman, and held him for two days before handing him over to Indian officials.
India's MiG-21s, while featuring some key upgrades, still are more than 30 years old. The Pakistani F-16 that the Indians shot down reportedly was a Block 52D model that Islamabad in 2005 ordered from the United States.
"The MiG-21 is in our inventory, why will we not use it?" Indian Air Chief Marshal BS Dhanoa rhetorically asked reporters when questioned about the aerial disparity.
To be fair, India in the 1990s upgraded its MiG-21s to the "Bison" standard with Western-style avionics, a new radar and radar warning receiver and compatibility with modern weapons. "[It] has got better weapons system, better air-to-air missiles," Dhanoa pointed out.
But the main reason India sent the MiG-21 into battle is that the type is still one of the most numerous in Indian air force service. "We fight with all the aircraft in our inventory," Dhanoa said.
Indeed, the aerial battle in which the MiG-21 and F-16 were shot down involved, on both sides, mixed formations of old and new fighters.
"The MiG-21 that was shot down on Feb. 27, 2019, was part of a formation of eight Indian fighters which included four Sukhoi 30s, two upgraded Mirage 2000s and two MiG-21 Bisons that were dispatched to engage a package of 24 [Pakistani air force] jets that included eight F-16s, four Mirage III aircraft, four JF-17 Thunders," David Cenciotti reported at The Aviationist.
India for years has been struggling to replace a large fleet of old, Russian-made warplanes. In 2018 the Indian air force operated 244 1960s-vintage MiG-21s and 84 MiG-27s that are only slightly younger.
The MiG-21s, in particular, are accident-prone. Since the first of 874 MiG-21s entered Indian service in 1963, around 490 have crashed, killing around 200 pilots.
New Delhi wants to spend around $18 billion building 115 new fighters to replace the old MiGs. The new planes would fly alongside European-designed Jaguars, French Mirage 2000s and Rafales, Russian MiG-29s and Su-30s, and India's own indigenous Tejas fighter in what Lockheed described as "the world’s largest fighter aircraft ecosystem."
Competitors for the 115-plane purchase include an upgraded F-16 that Lockheed Martin calls the "F-21," Boeing's F/A-18E/F, the Rafale, the European Typhoon, the Swedish Gripen E and the Russian MiG-35 and Su-35. Indian companies would assemble the new jets on license.
At the same time, Russia wants to sell to the Indians an upgrade package for New Delhi's Su-30s. The Su-30SM would benefit from many of the systems that manufacturer Sukhoi developed for the newer Su-35.
The complexity of acquisitions processes in New Delhi could force the Indian air force to operate for years or even decades longer a diverse mix of old and new fighters.
There's no reason this mixed force can't be effective in aerial combat, Cenciotti explained. An old fighter such as the MiG-21 can be deadly under the right circumstances.
Not always does the more modern and capable weapon system (in this case the PAF F-16) win. Several factors must be taken into consideration: pilot skills, support from other assets (including fighters and [airborne early warning] aircraft), ground radars, etc.
Above all, [rules of engagement] play an essential role: if the rules of engagement require a positive [visual identification] of the opponent, a fighter might be forced to come [within visual range] where a MiG-21 can be particularly threatening.