Tenerif .... MUMBAI!

[Evan]

That's simply an unrealistic POV to think that you can avoid even "extremely unlikely risks".
If you want to achieve that, you have to cancel basically all airline ops.

You’ve addressed the why not but not the why. If you need to have planes going around to avoid this scenario, you have a major problem with your air traffic control. Spacing arrivals at least 90 seconds apart does not equate with “cancel all airline ops” (you’re starting to sound like 3WE).

(Btw. I don't know what reverse thrust has to do in this scenario)

Longer stopping distance…?

And you must factor in human error. The FAA does. There is situational awareness, the time it takes or if it doesn’t happen at all. That can be a lot of runway. There is float, landing further down the runway. There is reaction time, which the FAA factors into stopping distance as an average, expected time. Then, and perhaps most importantly, there is stress and time compression related error. A pilot might touch down, realize the airplane ahead has rejected and choose to go-around. I know it’s the wrong move but check your aviation accident history and you will see a lot of wrong moves made by very experienced pilots under sudden urgent situations. Human factors. You do not want to create an environment that can lead to human error and accidents.

Now, can you tell me why spacing arrivals and departures at least a minute apart is “cancel all airline ops”?

[3WE]

***You can't be so naive to assume that e.g. the CAA hasn't considered every imaginable case (and most likely a lot more you haven't thought of) before approving the LHR & LGW procedures and it's pro and cons.***

Many years ago, ATL said this. Not exactly, but the concept. It’s a very important statement.

I enjoy discussing aviation as an outsider and appreciate when you, Bobby, ATL and others share reality.

We outsiders are all guilty of providing overly-simple, free advice to the aviation industry…hopefully, I think twice and am not_overly bold when I do…but then again, my nickname is 3BS.

Evan, however…

[bstolle]

Why not do that? Because extremely unlikely risks are introduced.
Why do that? .... (I've got nothing)

That's simply an unrealistic POV to think that you can avoid even "extremely unlikely risks".
If you want to achieve that, you have to cancel basically all airline ops.
Double engine failure on two engined airliner have happened, all engine failures on four engined airliners as well. etc.
Don't you think that e.g. the CAA hasn't considered every imaginable case (and most likely a lot more you haven't thought of) before approving the LHR & LGW procedures and it's pro and cons? E.g. you disregarded the risks of go-around related accidents, which is by an very large margin higher than your assumed reverser/ground spoilers/brakes malfunction. (Btw. I don't know what reverse thrust has to do in this scenario)

[flashcrash]

Note that, while 6000ft is more or less 2000m, that distance can be used in lieu of "the other aircraft has crossed the runway end". Not in lieu of "the other aircraft has departed".

The original article says the arriving aircraft crossed the threshold 22 seconds after the departing aircraft had begun its takeoff roll. The two aircraft were just 1670ft, or 500m, apart at closest approach, at which time the departing aircraft had not yet rotated. At rotation, the separation was just a few feet greater. The landing aircraft touched down 3 seconds later.

[Evan]

Assuming that the plane flew at that landing speed from the threshold to the touchdown point, the whole threshold to touchdown to stopping point journey would take 52 seconds.

And this is what gets me... Assuming that each plane landing or rolling on takeoff needs that runway to itself for less than a minute, what are they doing piling on like this? Is it really too impractical to enforce a 'sterile runway' rule?

An outcome like the ones you describe above extremely unlikely

Like Tenerife, you mean? Or soooo many other bad outcomes. One in a million is a lot of fatality. The entire reason I am so interested in aviation safety is that it actually works so well, despite enormous risks, and retains integrity when the rest of the human experiment is racing down the drain of corruption and lassitude. And it works because it does often consider extremely unlikely risks unacceptable. The philosophy seems to be asking 'why do that' as much as 'why not do that'.

An arriving plane and a departing plane sharing a runway.
Why not do that? Because extremely unlikely risks are introduced.
Why do that? .... (I've got nothing)

[3WE]

I had a flight into JFK break-off last minute in severe VMC because the pilot didn’t like the separation. The traffic ahead had landed but had not cleared the runway. That is a pilot from a strong safety culture. I wish they were all like that.

Good for you.

I’ve survived two airliner traffic go-arounds in severe VMC
One airliner traffic go-around in IMC
One missed approach in a regional turboprop
DONE one 172 go around when a departing dude apparently wasn’t listening to Unicom
TOLD another tower I was making a 360 because he had me and a Dash-8 aiming at each other on intersecting runways.
And watched and listened to plenty of successful squeeze plays AND less successful go arounds at Flyover in the TWA/Ozark glory days. One night at STL, a pilot pulled into position and then did something to the radio. The tower cleared them three times, finally saying immediate takeoff and then asked the landing plane to switch runways, to which they said “it’s too late now”. There was a good verbal jab when the plane in position checked in.

Spare us the attitude that you were blessed with one of the “few”, safety-minded, not_cowboy pilots. The system and people are pretty damn good, even though ATC sometimes gets folks too close. Pilots land or go around from squeeze plays and the passengers don’t did died every day.

I’m more worried about gross brain farts on intersecting runways and taxiways than an admittedly-spectacular, VMC squeeze-play or Gabieee’s long paragraphs of what-ifs.

[Gabriel]

Here, I’ll give you some shades of grey:

Departing aircraft rejects. Auto brakes. Rapid deceleration. Arriving aircraft touching down is not aware of this. Situational awareness delay. Then reaction time. Then the reverser/ground spoilers/brakes malfunction. The following occurs over a span of seconds.

shade a) Arriving aircraft attempts to stop but collides with the rejecting aircraft. Bad outcome.

shade b) Arriving aircraft attempts to get airborne again. Tenerife. Bad outcome.

shade c) Arriving aircraft manages to steer off the runway at damaging speed. Maybe only losing some gear and an engine in the process, Or maybe only slicing into the departing aircraft with one fuel-laden wing. Best outcome.

This scenario requires two factors. Most fatal accident do. Swiss cheese.

What the FAA seems to understand and you cannot is that all of these outcomes are possible when two aircraft are on the same runway in a high-energy state. And I’m not even getting into jetwash in the flare.

I had a flight into JFK break-off last minute in severe VMC because the pilot didn’t like the separation. The traffic ahead had landed but had not cleared the runway. That’s a pilot from a strong safety culture. I wish they were all like that.

To be fair, and while I still would not like it, if the European regulation allows the aircraft that landed ahead or the one that is taking off ahead to be on the runway if they are at least 2500m from the landing threshold, that would be an ample margin to make an outcome like the ones you describe above extremely unlikely. These are the layers of Swiss cheese:

0- 2500m is enough landing distance for most normal landings with moderate braking. I mean if you remove 1000 of the 2500m due twice-longer-than-normal flare, a deceleration of just 0.2G which is less than 4 kts/sec (a moderate deceleration, Autobrakes 2 in the 737) would let you to go from 150kts to 0 in the remaining 1500m. Note that I am combining an abnormally high landing speed, an abnormally long touchdown, and a normal but very moderate braking. That combo is a pretty thick slice of cheese. And you still have several more:
1- Assuming that the plane flew at that landing speed from the threshold to the touchdown point, the whole threshold to touchdown to stopping point journey would take 52 seconds. The plane ahead will most likely not be 2500m down the runway, the same spot that it was 52 seconds ago when the landing plane crossed the threshold.
2- The pilots will not just sit there looking the other plane static on the runway estimating that it will be tight or worse if they leave Autobrakes 2, and leave Autobrakes 2 being along the ride for the crash.
3- Even if any evasive maneuver is needed a the last moment because the layers #0, 1, 2 and 3 all failed, it would be a low speed event, maybe with an airplane stuck in the mud at worst. Not your "best outcome" above.

And I want to think that there are provisions in place such as if you have an overweight landing, a flapless landing, or a very high density altitude conditions, where you need a greater landing speed and greater stopping distance (layer #0 at risk), these operations would not be performed.

So why I still don't like it? It still has the crystal ball thing. It is easy to watch the video and see hoe long down the runway the plane landing / departing ahead was on the runway when the landing plane crossed the threshold. But it is very difficult to predict where it will be when you are clearing the landing airplane for landing. Now, withholding the landing clearance until the conditions are met (rather than clearing a plane for landing when another one is cleared or about to be cleared to land or take off in front of them on the same runway) would eliminate the crystal ball thing, rendering an accident almost impossible.

[Evan]

Thanks for your ongoing black and white insight.

2. Fixed. Just because of your certainty that a take off abort = no option for collision avoidance.

Here, I’ll give you some shades of grey:

Departing aircraft rejects. Auto brakes. Rapid deceleration. Arriving aircraft touching down is not aware of this. Situational awareness delay. Then reaction time. Then the reverser/ground spoilers/brakes malfunction. The following occurs over a span of seconds.

shade a) Arriving aircraft attempts to stop but collides with the rejecting aircraft. Bad outcome.

shade b) Arriving aircraft attempts to get airborne again. Tenerife. Bad outcome.

shade c) Arriving aircraft manages to steer off the runway at damaging speed. Maybe only losing some gear and an engine in the process, Or maybe only slicing into the departing aircraft with one fuel-laden wing. Best outcome.

This scenario requires two factors. Most fatal accident do. Swiss cheese.

What the FAA seems to understand and you cannot is that all of these outcomes are possible when two aircraft are on the same runway in a high-energy state. And I’m not even getting into jetwash in the flare.

I had a flight into JFK break-off last minute in severe VMC because the pilot didn’t like the separation. The traffic ahead had landed but had not cleared the runway. That’s a pilot from a strong safety culture. I wish they were all like that.

[3WE]

1. ***The arriving aircraft will be colliding with the departing aircraft if***

2. I often have no brain.

1. I will post a favorite Three Dog Night tune from upper grade school days at the bottom.

They will crash if the pilots deliberately make an effort to crash…otherwise in severe VMC conditions, you sort of steer away from the other aircraft and hopefully have type-specific training to turn off the autopilot.

Thanks for your ongoing black and white insight.

2. Fixed. Just because of your certainty that a take off abort = no option for collision avoidance.

Footnote: By the way, Evan, do we really want planes with underslung engines wantonly going around?…there’s all that trim and somatogravic illusions (Bernt, I’m being sarcastic here.)

https://youtu.be/PEy6968xO-I?si=fmrX727OM7nR2sXY

[bstolle]

Sigh, as usual Evan doesn't have the faintest idea what he's talking about.

[Evan]

I know neither the FAA nor the Indian rules but that's the way it's being used in Europe e.g. at LHR and LGW;

(a) When the runway-in-use is temporarily occupied by other traffic, landing clearance will be issued to an arriving aircraft provided that at the time the aircraft crosses the threshold of the runway-in-use the following separation distances will exist:
(i) Landing following landing - The preceding landing aircraft will be clear of the runway-in-use or will be at least 2500 m from the threshold of the runway-in-use.
(ii) Landing following departure - The departing aircraft will be airborne and at least 2000 m from the threshold of the runway-in-use, or if not airborne, will be at least 2500 m from the threshold of the runway-in-use.

Are European aircraft equipped with crystal balls? That’s a lot of ‘will be’ in those regulations. How about this:

(iii) The arriving aircraft will be colliding with the departing aircraft if the departing aircraft rejects takeoff and the arriving aircraft experiences any of the conditions common to runway overrun incidents.

What? A combination of factors? When has that ever happened? Oh, right, Tenerife…

The FAA regulations make sense if safety is truly your concern. No departing and arriving aircraft can occupy the runway at any given time. No brainer.

[bstolle]

I know neither the FAA nor the Indian rules but that's the way it's being used in Europe e.g. at LHR and LGW;

(a) When the runway-in-use is temporarily occupied by other traffic, landing clearance will be issued to an arriving aircraft provided that at the time the aircraft crosses the threshold of the runway-in-use the following separation distances will exist:
(i) Landing following landing - The preceding landing aircraft will be clear of the runway-in-use or will be at least 2500 m from the threshold of the runway-in-use.
(ii) Landing following departure - The departing aircraft will be airborne and at least 2000 m from the threshold of the runway-in-use, or if not airborne, will be at least 2500 m from the threshold of the runway-in-use.

[Gabriel]

Even both planes can be legally touching the pavement at the same time. That's the 'land after' procedure.
In this case the official minimum distance would have been 2000m.

Source? Is that in India? Because, in the US, as far as I know, this applies:

FAA Order JO 7110.65AA - Air Traffic Control

3-10-3. SAME RUNWAY SEPARATION

a. Separate an arriving aircraft from another aircraft using the same runway by ensuring that the arriving aircraft does not cross the landing threshold until one of the following conditions exists

2. The other aircraft has departed and crossed the runway end. If you can determine distances by reference to suitable landmarks and the other aircraft is airborne, it need not have crossed the runway end if the following minimum distance from the landing threshold exists:
(c) When either is a category III aircraft- 6,000 feet.

Note that, while 6000ft is more or less 2000m, that distance can be used in lieu of "the other aircraft has crossed the runway end". Not in lieu of "the other aircraft has departed". Which means that both being on the runway at the same time would be illegal.

[bstolle]

But in VMC, how did it ever get to that point?

As 3WE has pointed out, the landing plane may be asked to slow down, or ATC asked if the landing traffic can maintain own separation. If the departing traffic accelerates slower than expected, the officially required 2000m quickly reduce to e.g. 1500m. Risking a go-around at the point isn't a 100% option either.

[bstolle]

My ass hat opinion was that as long as only one was touching the pavement it was fine, but Gabe told me it was illegal.

I’d also ask if going around is that much better as two planes FLY in close proximity and speeds.

Even both planes can be legally touching the pavement at the same time. That's the 'land after' procedure.
In this case the official minimum distance would have been 2000m. Difficult to tell, how far the departing traffic is away as the IndiGo touches down, but it looks like it's less than 2000m.
Since the IndoGo pilot clearly had the departing traffic in sight and could maintain sufficient separation, landing was not a bad option.
As you correctly observed, a go-around in this case would have been really dangerous.

I still remember a similar case with significantly less separation when my Captain decided to land really close behind a departing MD-80.
What he underestimated was the violent jet wash we encountered during the flare!