I am hoping there is a factual answer to the question, if not, mods feel free to move this.
So there is this in the news : U.S. fighter jets fly near Iranian passenger plane, state media says
Trying to understand the sequence of events that lead up to such inspections. And what are the fighter jets looking for ?
My guess is, verifying that they are a passenger jet and not a warplane.
That being said, if they can’t verify from a long distance via radar what kind of airplane it is, and must get up close to see with one’s own eyes, it seems to speak really poorly of radar capabilities.
Yeah, If you can see it, it is not a stealth plane sneaking up on you.
You can check it that airline has a scheduled flight in that area. You can see there isn’t a great big bomb strapped to the fuselage.
From your cite: "
Two U.S. Department of Defense officials said the Iranian airline had deviated from the civilian air corridor…"
and "
U.S. Central Command, which oversees American troops in the region, said the F-15 aircraft was conducting a visual inspection of the Iranian plane at approximately 1,000 meters (around 1,094 yards) when it passed near the Tanf garrison in Syria where coalition forces are present."
So, the airliner was, according to the US, flying outside of the box it was supposed to be flying in, potentially near an area where US troops were, and 2 F-15s went over to take a look at the contact. Until someone like @LSLGuy or another been there-done that poster chimes in differently, the radar return from even a sophisticated radar like an Eagle’s AN/APG 63 V whatever, is a blip. The blip doesn’t tell the operator what kind of airplane it’s returning from, just its distance from the emitter, its relative speed to the emitter, and how strong the return is (?) The pilot needs to see the aircraft (with their eyes, or some slaved magnifying sight) to know more.
Had the pilots not inadvertently triggered the TCAS (collision warning system) on the airliner, this wouldn’t be news. It would be interesting to know what happened. I would have thought the Eagle pilots would have tried radio communication with the airliner before getting that close, then maybe the TCAS going off wouldn’t have triggered the desire by the airliner pilots to maneuver abruptly.
Here’s a batch of factors not adding up to a coherent essay.
Even setting aside any he-said-she-said falsification or posturing, there’s a lot of ambiguities and complexities here. Somebody screwed up along the way somewhere, but we in the public sure don’t know who or how yet.
Procedure back in my day would have the fighter maneuver so as to try to avoid triggering the airliner’s TCAS. As well we’d typically adjust our switchology to preclude triggering their TCAS at all. Then again, that was peacetime training 30 years ago, not guys working in an active war zone in very different airplanes w (probably) fancier equipment.
If the fighter is in a big enough hurry about a worrisome enough target, just getting close enough fast enough to confirm the target’s lack of hostile capability is the only thing that really matters. If that results in a high rate of closure in close, so be it.
We also don’t know what the weather was; the Mideast can be real hazy where you have to get pretty close to see anything.
Or maybe the F-15 drivers, like the Vincennes 32(!) years ago, were a little bunch too cowboy for their britches.
The articles I’ve seen are a little ambiguous about which collision avoidance system is involved and which aircraft experienced the alarm. The OP’s article says the fighter’s “automated collision avoidance system” triggered and they presume the airliner’s did too.
TCAS is the civil standard all airliners worldwide have. But does the F-15 have that? We sure didn’t back in my day.
Does the F-15 have a totally different system based on its own air to air radar that would warn for excessive closure rates in close but leave the airliner unaware? Does the Iran Air airliner have a RWR receiver that would warn them that a fighter (or SAM) radar has them targeted? Certainly US airliners don’t have that, but Iran Air, El Al, etc., operate in more dangerous neighborhoods & might well.
In response to a TCAS alert for any reason, the appropriate maneuver by an airliner is prompt but smooth. Bouncing people off the ceiling, throwing them to the floor, etc., is gross over-controlling by the airline pilots.
Response to gross cowboying by an interceptor OTOH could hurt folks in the back pretty easily. See wiki for a similar incident with the shoe on the other foot.
Older F-15s were not equipped with radios that can connect to airliner radios. So any commo from those sorts of F-15s to airliners would have to be relayed through ATC. Later F-15s did have airliner-appropriate radios. Did these particular F-15s have airliner-appropriate radios? The public doesn’t know yet.
The fact the airliner was not where the US military expected it to be implies (not guarantees) they were off course. Which in turn implies they weren’t talking to a radar -equipped ATC authority of any country or that ATC authority would probably have noticed them off course & done something about it.
Even with fighters with airliner-compatible radios there’s the question of which frequencies to communicate on. For any given blob of airspace there is exactly one ATC authority that’s managing it. But which frequency is in use in that blob of air varies from time to time & only by contacting the controlling agency and asking can one know for sure. Knowing that frequency wouldn’t help in the event the airliner had goofed and was on the wrong frequency or had turned down the volume for some reason. It happens every day.
There is also the concept of the “Guard” or emergency frequency that everybody is supposed to monitor all the time everywhere and is a “universal hailing frequency” in extremis. As above, something less than 100% of airliners actually monitor it 100% of the time. Due to sloth or an honest switch error. The radio commonly used for monitoring Guard is also used for other things at various points in the flight and may have been legitimately in another use at the moment that mattered, or may have been simply misset.
The article says the Iranian pilot said that the fighters had identified themselves as American, not Israeli. That implies they were talking to each other at some point, although whether that was before or after the passengers were injured isn’t stated in the article.
I find it a little surprising that the interior pix show all the window shades up. That’s sure not how US airliners look inside. Then again, after a scary close encounter you might expect to find all the pax anxiously scanning the skies looking for the next wave of interceptors.
If the fighters were scary close alongside I’d expect there to be at least one passenger photo of that. If such a photo existed the various Iranian press releases would certainly have included it and legitimately so. That implies (not guarantees) that the fighters were where the passengers couldn’t see them.
We certainly used various avenues of approach to the target that were intended to keep us invisible to passengers, the pilots, dedicated side / top / bottom observers carried aboard many military aircraft, and for targets suspected of having tail guns, outside the field of view of the gunner’s windows & gun aiming radars. Time permitting.
Lots of factors to consider.
Absent any hard data I’m going to speculate it was both over-eager F-15s and over-reactive Iran Air pilots. Bad luck they came together on the same day.
These are the kinds of bad local luck meets a bad global situation events that have triggered instant crises every few years all over the world since WWII ended. And will continue to do so. It becomes a question of when & where, not if or whether. That’s a dumb way to run a planet.
Thank you @LSLGuy for the detailed analysis
thank you LSLGuy for the background. The Dope always has good people.
Frankly, when I heard about this, I figured that the Iranian pilots overreacted when they realized they were being shadowed by US fighters. Given recent events in the area, Iranians have good reason to be jumpy about US intentions (and vice versa). I am guessing that two pilots were cruising along and Oh Shit armed fighters! and they overreacted. I know I would. I am just glad the worst that came out of it was a bloody nose or two.
Possibly dumb question here, regarding the radar return from the airliner: Isn’t it supposed to have a transponder onboard, that returns a number given to the plane before takeoff, so that the plane can be more easily identified? Especially by ATC.
Now, these transponders can be set to anything, so it’s wise for the military to send up a fighter or two to verify if it’s actually an airliner or not. But I haven’t heard any mention of what the transponder might have indicated. (Maybe I missed it.) Thanks-
tldr: Transponders assume everybody is playing nice. Militaries in war zones assume everybody else is NOT playing nice. The uneasy interface between those two worlds is why interceptors go see for sure.
Long version …
A reasonable question.
Transponders are 1950s tech designed for 1950s volumes of traffic. And for no bad actors involved in the process.
The ATC agency controlling the airplane gives it a code to set into the transponder. Only the ATC agency knows what code they assigned to any given aircraft at any given moment. These codes are temporary and recycled very few hours. In busy airspace (i.e. not where they were), it’s common to use multiple codes per flight to avoid duplicate codes with other passing airplanes.
Any pilot can set any code into his/her transponder at any time. Or no code at all. Or turn it off. It takes everybody cooperating for the ATC system to work.
At least in my day fighters did not have the capability to interrogate a transponder to retrieve whatever code is set.
So putting it all together, the US military ground radar could presumably see the transponder and interrogate the code. But would have no way to determine what flight number, call sign, or aircraft type that code was supposedly attached to. Other than by calling Iranian ATC on the phone to ask.
If for argument’s sake we assume the Iranians were up to no good, they’d certainly not truthfully cooperate with such a request. And even if in this instance they were NOT up to no good, the US military couldn’t assume so.
So fighters would have to go look in any case.
One thing to keep in mind in all of this is that Mahan Airlines, while technically a privately owned company, is well known for smuggling weapons and military parts for the Iranian military in violation of sanctions imposed by the U.S. and other countries. They also transport weapons and operatives for Hezbollah and smuggle weapons for Iran’s Islamic Revolutionary Guard. This isn’t just an innocent passenger transport company like Iran claims it is. Because of this, the company is actually banned from landing in many Western countries, like Italy and Germany.
Mahan Airlines does actually function as a real airline, but then you never really know what’s inside their cargo hold. I have no way of knowing what happened in this case, but it’s possible that the fighter jet took a closer look to verify that the plane actually had passengers on it and wasn’t just hauling illegal cargo.
It’s also difficult to tell at a distance if a plane is a passenger plane or if it is some sort of military plane. You’re not going to confuse a 737 with an F-15, but take a look at the P-8A Poseidon. That’s basically a military version of the 737. Just because it looks like a passenger plane from far away doesn’t mean that it actually is a passenger plane.
I think you’re dramatically overestimating the capability of air defense radars. Most of what air traffic controllers know about planes is due to their transponders telling them what sort of plane it is, etc… And I don’t doubt the Iranian airliner had one running as well.
But radar itself could probably tell you that the object’s radar return is roughly like an airliner might be. But it can’t probably tell a B-52 from a 747, especially at longer ranges, etc… so air forces will fly interceptors up there so the pilots can eyeball what exactly is going on. And in this case, the airliner wasn’t answering the radio either.
Here’s an example of where the USAF got caught in some shenanigans with a KC-10 Extender (a DC-10 tanker version) and a couple of F-117 stealth fighters. Basically they overflew Austrian airspace with the F-117s flying very close formation, so that the Austrians couldn’t see them as separate planes on radar. But the Austrians flew up there and saw 3 planes not one…
That’s exactly why we flew the fighters up there- there’s a 55 mile "deconfliction zone around some US base, and the airliner passed into it and didn’t answer the radio messages. So they flew some F-15s up to check it out. And supposedly they didn’t get any closer than 1000 meters (1 kilometer / 3280 feet) to the airliner, so it’s not like they did some Top Gun nonsense and flew super-close either.
Certain modern fighters can interrogate transponders and some have capabilities that enable them to ID what they are pinging with the radar set (20 years as an avionics tech). It is still SOP to Mk 1 Eyeball a potential threat in cases like this. No one wants to repeat KAL 007, especially in the Middle East.