Air To Air Combat Has Been Very Rare For A Generation

The stereotypical dog fight is all but dead. Just one pilot still serving in the U.S. military as a pilot has ever participated in a dog fight that resulted in a manned fixed wing aircraft in flight that was part of the fight being shot down. The U.S. hasn't had a dog fight involving guns instead of missiles since 1975.

Dog Fights Have Grown Very Rare

In the last 28 years (since the end of the Gulf War) not more than 54 manned aircraft were shot down by other aircraft in the entire world. At least 2 were from a friendly fire incident. Many are downed helicopters. See here. 

Just one U.S. fixed wing aircraft has been shot down by another aircraft since the end of the Vietnam War (1975) when a U.S. Navy F/A-18 piloted by Scott Speicher was shot down in air to air combat on January 17, 1991 during the early days of the Gulf War. There is been just two incidents in which a U.S. fixed wing aircraft has shot down another fixed wing aircraft in flight since the Gulf War which ended in 1991, one in Kosovo in 1999 and one in Syria in 2017.

There hasn't been a fighter ace (a pilot who has made five or more career kills of enemy aircraft in air to air combat) actively serving as a pilot the U.S. military for decades.

At least some of the aircraft crews survived in a fair number of the incidents involving fixed wing aircraft that were shot down. 

Missiles Have Replaced Slug Throwers

A key factor in the modern trend this has been the use of guided missiles. Most of these are one shot, one kill incidents, with the first shot often fired before the other pilot knows that he engaged in air to air combat at that moment.

The last time a manned fixed wing aircraft in flight was shot down by another manned fixed wing aircraft, with anything other than a missile, anywhere in the world, by any country, was on October 5, 1982 when a South African fighter pilot shot down a Cuban fighter with his canon in the South African border war (about 37 years ago). Prior to that there were a number of such dog fights in the Vietnam War (which ended in 1975) and in the Yom Kippur War in Israel (in 1973). See here.  

There are a number of incidents of helicopters being taken down with slug throwers from other aircraft, however, most often with the 30mm canons of the A-10 ground attack fighter. There are also cases of ground targets being destroyed with an armed fixed wing aircraft's canons.

The lion's share of military aircraft that are shot down in flight in the modern era are shot down by ground to air fire, most often, but not always with anti-aircraft missiles, and the aircraft shot down are disproportionately helicopters and unmanned drones.

What Does The Modern Air Force Do?

This doesn't mean that armed aircraft are irrelevant. But, armed aircraft are now almost entirely deployed in conflicts where one side or the other in a conflict controls the air space of the theater of battle. And, where there are air to air combat campaigns they have been very brief - a matter of a few weeks at most.

Guided air to ground missiles, and long range sea or ground launched guided missiles, are one of the defining aspects of modern warfare, and close air support of ground troops continues to be a significant military mission. 

As of August 29, 2017, "every deployed squadron averages at least a 97 percent hit rate" when using guided missiles and/or smart bombs, a dramatic reduction from the era of non-guided bombs and missiles. This is a recent development. In the 1995 campaign in Bosnia, 98% of bombs dropped by American aircraft were guided.  But, while "Operation Desert Storm in 1991 often invokes images of stealth aircraft and laser-guided munitions. However, only 8 percent of all bombs dropped during that war were guided. . . . In Desert Storm, the F-117 (flown by highly experienced pilots) was lauded by an unprecedented (and inflated) 80 percent hit rate." In the Vietnam War, "to hit a half-dozen targets, aircraft packages were generally built around 16 strike aircraft (escorted by other fighters performing escort and suppression of enemy air defenses)." In the Gulf War and Vietnam, Air Force pilots flew 19-20 hours a month, now they fly 10 hours a month.

It now takes far fewer missions to hit a given number of targets, and there is very little ordinance wasted in strikes that don't hit their targets.

Effective countermeasures could limit this effectiveness. 

If the enemy can’t stop your weapons, you need to send just one to have 95 percent confidence of hitting any given target. But if the enemy can stop a significant fraction of your smart bombs, say 20 percent, you need to send two to achieve that same 95 percent confidence. If your weapons have only a 50-50 chance, you need to send five. . . .  

A staggering 96 percent of the precision weapons the Pentagon has bought since 9/11 have been “direct attack” munitions. These weapons are relatively short-ranged. For example, the new Small Diameter Bomb (SDB) II has wings to glide up to 40 nautical miles from the aircraft that launches it. The older and larger Joint Direct Attack Munition (JDAM) can glide just 13 nm. 

Against a low-tech adversary like the Islamic State, a US aircraft 13 miles away might as well be on the moon. Against an adversary with modern anti-aircraft weapons, however, a US aircraft that comes within 13 or even 40 miles is begging to be shot down. . . . 

[W]e have far too few long-range weapons such as cruise missiles, which can be fired from outside enemy air defenses’ range, and the ones we do have are far too expensive to buy in bulk. The average direct-attack bomb bought since 2001 costs $55,500; the average long-range precision-guided weapon costs $1.1 million, twenty times as much.

But, the vast majority of wars, not just involving the U.S., but everywhere in the world, are asymmetric, not competitions between "near peers" where effective long range anti-aircraft and anti-missile defenses aren't present.

Also, I believe that I read recently that in a recent month in the war in Afghanistan, most of the U.S. airstrikes were carried out by drones, which makes the costs of losing aircraft much more tolerable.