I’m a pilot, I’m familiar with these systems and how they work.
So 1. eyes. VMC prevailed, I’m assuming the helicopter was operating under VFR; in fact I would find it extremely weird if they were under IFR because if so they should have been properly sequenced. According to ABC News, the helicopter was in radio contact with the tower who advised the helicopter of the approaching airliner and asked if they had it in sight. With few clouds at 1100 feet and visibility of better than 10 statute miles, the helicopter should have been able to see an airliner with position lights, strobes and landing lights on, even if the airliner couldn’t see the helicopter. At this point I should mention, there are rules about who gets the right of way in the sky, generally it’s less maneuverable aircraft get right of way over more maneuverable aircraft, helicopters must yield to airplanes, helicopters can stop, airplanes can’t. So it was the job of the helicopter to see and avoid. Which they apparently failed to do.
Also, at 300 feet up, this collision took place less than a mile from the runway, the tower should have been able to see both aircraft visually.
Radar. Secondary surveillance radar is decades old technology, it has its roots in World War 2. It is possible the helicopter was so low that it wasn’t visible on radar with terrain and whatnot.
TCAS. This is a system installed on the airliner that basically works as its own surveillance radar, capable of interrogating any Mode C Transponder equipped aircraft, which is required equipment to fly in this airspace. The airliner apparently had line of sight to the helicopter, after all they hit the damn thing, so they should have been able to see the helicopter on TCAS, which should have warned them to climb to avoid the collision. This may not work if the airliner had their TCAS equipment in standby mode, or if the helicopter wasn’t squawking. The turbine-powered transport aircraft with more than 30 passenger seats is required to carry TCAS, so they DID have it on board.
ADS-B. Each aircraft carries a GPS receiver and a transmitter that automatically transmits their location in 3D space; it’s more accurate than surveillance radar and works everywhere the aircraft is. ADS-B Out is also required equipment to operate in this airspace; the tower should have been able to see the helicopter’s position very accurately through ADS-B. The airliner should have been, but I don’t think is yet required to, carry ADS-B in, which also should have been able to see the helicopter.
So. Why did all these things simultaneously fail? Why was the helicopter even close to the approach path in the first place, they were apparently in radio contact with the tower, why were they allowed anywhere near there? Why did they fail to maintain visual separation from other traffic given warnings from ATC? Why did surveillance radar, TCAS and ADS-B, all of which should have been working, fail to prevent the collision?
Why did the iceberg penetrate all 6,000 hulls? If only the ship had 6,001 hulls!
I’m assuming the helicopter was operating under VFR
They were, that’s been confirmed.
With few clouds at 1100 feet and visibility of better than 10 statute miles, the helicopter should have been able to see an airliner with position lights, strobes and landing lights on, even if the airliner couldn’t see the helicopter.
Yeah. Looking down, presumably through the floor of the aircraft, and seeing the lights of the helicopter against the dark backdrop and all of the different stationary and flashing lights that is Washington DC, would have been totally impossible.
Why the helicopter didn’t see the airplane after being specifically advised of that specific aircraft, I don’t know, but like I say, shit happens sometimes. Maybe he heard the radio message but just didn’t know up from down at that exact moment and was working on it. Maybe they saw a different airplane and thought it was that one. Maybe they saw it, but had trouble maneuvering away from it and a few seconds’ delay was all it took. The news did mention that it was a training flight, so the helicopter pilot fucking up is extra possible even above the possible that it already was.
the tower should have been able to see both aircraft visually
Wouldn’t it be pretty unusual for the controller that was talking to them to be looking anywhere other than their radar? Maybe if someone was staring out the window right at that specific situation right at that specific time, they might have seen it coming, but I don’t think that’s the usual behavior at all times for the person who’s talking with the pilots. It being at night and super-low so the lights of the helo can blend in confusingly with the backdrop lights just adds more unlikeliness.
Why they didn’t see the collision about to happen on radar is a separate question, but like you said, they were low to terrain.
TCAS
Does TCAS get disabled below certain altitudes or close to the runway? I know EGPWS does, which has caused some accidents in the past. Presumably, the TCAS isn’t squawking at you while you’re taxiing that you’re about to hit the next aircraft in front of you, so when does it get cut off? I have no idea, I’m just speculating.
So. Why did all these things simultaneously fail? Why was the helicopter even close to the approach path in the first place, they were apparently in radio contact with the tower, why were they allowed anywhere near there? Why did they fail to maintain visual separation from other traffic given warnings from ATC? Why did surveillance radar, TCAS and ADS-B, all of which should have been working, fail to prevent the collision?
This question I have no idea. My guess is that there’s no unified explanation, it was just a confluence of failures of a bunch of different things that each could have prevented it, and people just got really unlucky which happens sometimes. But that’s purely just uninformed speculation as to the answer to a pretty good question.
Edit: Oh, I completely missed this:
Do you have a source for this?
I’m a pilot, I’m familiar with these systems and how they work.
That wasn’t quite my question. You said the helo was invisible to TCAS / radar / etc, and I interpreted that as meaning it was some kind of special helicopter that was, well, invisible to radar. Now that I’m reading it in context, I get the point that you were making, but I took it seriously initially, as meaning it was some kind of military technology involved making it harder to see on radar or something.
TCAS systems will stop issuing RAs (verbal instructions to the pilots, such as ASCEND ASCEND) below 1,000 feet AGL so that it doesn’t steer anyone into terrain. I’ve never flown an aircraft equipped with TCAS, but it is my understanding that it would be switched to standby mode after taxiing off the runway, as you do with a Mode C transponder.
So yeah, in that case my official prediction for the way it will have turned out to have happened is:
Airplane sees helicopter - No way.
Helicopter sees airplane - Pilot fucked up.
Radar - Too low to terrain.
TCAS - Too low.
ADS-B - Could be one of the aircraft’s equipment wasn’t operating / present, or could be ATC fucked up. They could have just been looking at something else, doing their job in the busy airspace, and not seen two little dots out of dozens of others on their screen that were getting too close to each other. They’d also done everything they needed to do to very formally pass responsibility off to the helo pilot, so they’re allowed to preserve their mental bandwidth for other situations at that point, and it’s the pilot’s job to avoid the crash.
Airplane sees helicopter. Should have been possible several minutes before the collision, the airplane was approaching from the south-southeast and the helicopter from the North, at some point they were a couple miles apart and should have been able to see each other. Air traffic control should have known about both of them from the time they were at least 10 miles apart. It’s not like one of them suddenly pulled into traffic from behind a bus. The airliner would have been on an IFR flight plan and probably mostly heads down, and there’s a good chance the helicopter would have been lost in the city lights.
The crew of the helicopter has no excuse for missing a CRJ-700 with all it’s lights on against the black night sky after ATC told them where it was. The jet would have been at their 11 o’clock slightly high,
Maybe, I’ve spent no time in a TRACON or tower to tell you exactly what they can and cannot see, all I know is I’ve heard “radar contact” several thousand times in my life.
Too low for TCAS to verbally tell them to swerve; it probably still showed the relative position of the helicopter, unless one or the other wasn’t switched on.
I kinda wonder if the helicopter wasn’t running ADS-B. ADS-B is not encrypted (because good luck with that) so there are privacy/security concerns with it. Unlike Mode A or C transponders which only broadcast a 4-digit octal code, ADS-B sends information about the aircraft, it’s how people are able to track Elon Musk or Taylor Swift’s jets. This graphic from Wikipedia gives an ADS-B derived flight path for the jet, and an “MLAT” track (whatever that is) and an “approximate flight path” for the helicopter, so it’s possible it wasn’t transmitting ADS-B because military. Which would undermine the effectiveness of anti-collision systems a bit, no?
They’d also done everything they needed to do to very formally pass responsibility off to the helo pilot,
An aircraft operating under VFR is always responsible for collision avoidance anyway. It is my understanding that the electronic systems like radar and ADS-B have systems that will sound an alarm if aircraft get too close to bring the very busy controller’s attention to a critical situation. I wonder if this happened. Either way if you’ve got two aircraft getting that close to each other a half mile from the runway it’s time to look out the window, that’s why the tower is a tower.
They’re going to find the main contributing factor to the crash is pilot error on the part of the helicopter’s PIC. Why none of the other systems worked either is going to be an interesting read.
I’m a pilot, I’m familiar with these systems and how they work.
So 1. eyes. VMC prevailed, I’m assuming the helicopter was operating under VFR; in fact I would find it extremely weird if they were under IFR because if so they should have been properly sequenced. According to ABC News, the helicopter was in radio contact with the tower who advised the helicopter of the approaching airliner and asked if they had it in sight. With few clouds at 1100 feet and visibility of better than 10 statute miles, the helicopter should have been able to see an airliner with position lights, strobes and landing lights on, even if the airliner couldn’t see the helicopter. At this point I should mention, there are rules about who gets the right of way in the sky, generally it’s less maneuverable aircraft get right of way over more maneuverable aircraft, helicopters must yield to airplanes, helicopters can stop, airplanes can’t. So it was the job of the helicopter to see and avoid. Which they apparently failed to do.
Also, at 300 feet up, this collision took place less than a mile from the runway, the tower should have been able to see both aircraft visually.
Radar. Secondary surveillance radar is decades old technology, it has its roots in World War 2. It is possible the helicopter was so low that it wasn’t visible on radar with terrain and whatnot.
TCAS. This is a system installed on the airliner that basically works as its own surveillance radar, capable of interrogating any Mode C Transponder equipped aircraft, which is required equipment to fly in this airspace. The airliner apparently had line of sight to the helicopter, after all they hit the damn thing, so they should have been able to see the helicopter on TCAS, which should have warned them to climb to avoid the collision. This may not work if the airliner had their TCAS equipment in standby mode, or if the helicopter wasn’t squawking. The turbine-powered transport aircraft with more than 30 passenger seats is required to carry TCAS, so they DID have it on board.
ADS-B. Each aircraft carries a GPS receiver and a transmitter that automatically transmits their location in 3D space; it’s more accurate than surveillance radar and works everywhere the aircraft is. ADS-B Out is also required equipment to operate in this airspace; the tower should have been able to see the helicopter’s position very accurately through ADS-B. The airliner should have been, but I don’t think is yet required to, carry ADS-B in, which also should have been able to see the helicopter.
So. Why did all these things simultaneously fail? Why was the helicopter even close to the approach path in the first place, they were apparently in radio contact with the tower, why were they allowed anywhere near there? Why did they fail to maintain visual separation from other traffic given warnings from ATC? Why did surveillance radar, TCAS and ADS-B, all of which should have been working, fail to prevent the collision?
Why did the iceberg penetrate all 6,000 hulls? If only the ship had 6,001 hulls!
They were, that’s been confirmed.
Yeah. Looking down, presumably through the floor of the aircraft, and seeing the lights of the helicopter against the dark backdrop and all of the different stationary and flashing lights that is Washington DC, would have been totally impossible.
Why the helicopter didn’t see the airplane after being specifically advised of that specific aircraft, I don’t know, but like I say, shit happens sometimes. Maybe he heard the radio message but just didn’t know up from down at that exact moment and was working on it. Maybe they saw a different airplane and thought it was that one. Maybe they saw it, but had trouble maneuvering away from it and a few seconds’ delay was all it took. The news did mention that it was a training flight, so the helicopter pilot fucking up is extra possible even above the possible that it already was.
Wouldn’t it be pretty unusual for the controller that was talking to them to be looking anywhere other than their radar? Maybe if someone was staring out the window right at that specific situation right at that specific time, they might have seen it coming, but I don’t think that’s the usual behavior at all times for the person who’s talking with the pilots. It being at night and super-low so the lights of the helo can blend in confusingly with the backdrop lights just adds more unlikeliness.
Why they didn’t see the collision about to happen on radar is a separate question, but like you said, they were low to terrain.
Does TCAS get disabled below certain altitudes or close to the runway? I know EGPWS does, which has caused some accidents in the past. Presumably, the TCAS isn’t squawking at you while you’re taxiing that you’re about to hit the next aircraft in front of you, so when does it get cut off? I have no idea, I’m just speculating.
This question I have no idea. My guess is that there’s no unified explanation, it was just a confluence of failures of a bunch of different things that each could have prevented it, and people just got really unlucky which happens sometimes. But that’s purely just uninformed speculation as to the answer to a pretty good question.
Edit: Oh, I completely missed this:
That wasn’t quite my question. You said the helo was invisible to TCAS / radar / etc, and I interpreted that as meaning it was some kind of special helicopter that was, well, invisible to radar. Now that I’m reading it in context, I get the point that you were making, but I took it seriously initially, as meaning it was some kind of military technology involved making it harder to see on radar or something.
TCAS systems will stop issuing RAs (verbal instructions to the pilots, such as ASCEND ASCEND) below 1,000 feet AGL so that it doesn’t steer anyone into terrain. I’ve never flown an aircraft equipped with TCAS, but it is my understanding that it would be switched to standby mode after taxiing off the runway, as you do with a Mode C transponder.
Got it, that makes sense.
So yeah, in that case my official prediction for the way it will have turned out to have happened is:
Airplane sees helicopter. Should have been possible several minutes before the collision, the airplane was approaching from the south-southeast and the helicopter from the North, at some point they were a couple miles apart and should have been able to see each other. Air traffic control should have known about both of them from the time they were at least 10 miles apart. It’s not like one of them suddenly pulled into traffic from behind a bus. The airliner would have been on an IFR flight plan and probably mostly heads down, and there’s a good chance the helicopter would have been lost in the city lights.
The crew of the helicopter has no excuse for missing a CRJ-700 with all it’s lights on against the black night sky after ATC told them where it was. The jet would have been at their 11 o’clock slightly high,
Maybe, I’ve spent no time in a TRACON or tower to tell you exactly what they can and cannot see, all I know is I’ve heard “radar contact” several thousand times in my life.
Too low for TCAS to verbally tell them to swerve; it probably still showed the relative position of the helicopter, unless one or the other wasn’t switched on.
I kinda wonder if the helicopter wasn’t running ADS-B. ADS-B is not encrypted (because good luck with that) so there are privacy/security concerns with it. Unlike Mode A or C transponders which only broadcast a 4-digit octal code, ADS-B sends information about the aircraft, it’s how people are able to track Elon Musk or Taylor Swift’s jets. This graphic from Wikipedia gives an ADS-B derived flight path for the jet, and an “MLAT” track (whatever that is) and an “approximate flight path” for the helicopter, so it’s possible it wasn’t transmitting ADS-B because military. Which would undermine the effectiveness of anti-collision systems a bit, no?
An aircraft operating under VFR is always responsible for collision avoidance anyway. It is my understanding that the electronic systems like radar and ADS-B have systems that will sound an alarm if aircraft get too close to bring the very busy controller’s attention to a critical situation. I wonder if this happened. Either way if you’ve got two aircraft getting that close to each other a half mile from the runway it’s time to look out the window, that’s why the tower is a tower.
They’re going to find the main contributing factor to the crash is pilot error on the part of the helicopter’s PIC. Why none of the other systems worked either is going to be an interesting read.