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Comment by madaxe_again | Hacker News Reader

I am slightly scratching my head as to why, unless the pilots were only qualified for VFR.

I learned to fly with the RAF as an air cadet. I vividly recall the first lesson in which my instructor whipped out a piece of cardboard, covered the windscreen, and said “land”.

It turns out that as long as you’ve ILS, you can do it with zero vis.

It looks like they had ILS available: https://worldaerodata.com/wad.cgi?id=ET86469

I can’t help but think a blind landing is safer than depressurising a cabin full of passengers.

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I'm 100% sure they weren't only qualified for VFR. Every airline pilot is instrument rated, and there are no places that will give you a 737 type rating without IR.

Even when flying on instruments you still land visually, unless the aircraft is cat iii / autoland capable, the crew is certified and current and the airport has cat iii procedures in effect. Probably they didn't have one of these and didn't want to land with zero visibility.

Depressurizing at 8500ft is a good choice, the cabin is normally pressurized to the equivalent of 8000ft outside air pressure. So what they did was basically open the outflow valves and passengers wouldn't have noticed a thing.

I've heard from a couple of sources that it is possible to land in zero visibility by manually following the localiser to the ground. Only from light piston types though.

Doing it in a commercial airliner full of passengers would absolutely be a last resort.

It is possible, but not legal. And you cannot really flare based on just the glideslope.

As an absolute last resort in a small piston you can try to do what we learned to do in case of a night landing where all lighting etc fails: Fly it slightly nose up, no flaps, with a 100 ft/min descend and wait until you hit the runway. You will basically fly it into the runway at a speed that doesn't break anything. Only works for small planes on a big runway.

Yes, is very similar to a glass water landing in float planes. For a number of reasons the glideslope is unreliable below minimums anyway.

The legality doesn't matter much if you are doing it in an emergency (say unforcast fog shutting down all runways within the aircraft's remaining range).

True, they recommended LPV in this case. That remains quite stable all the way to the ground. It also doesn't require any ground equipment and this scenario is only likely in case of a total power loss at a remote airport.

No, you are not allowed to do an ILS landing with zero ground visibility. And I doubt you get the flare right without any visiblity.

All available categories have a decision height > 0ft: https://en.wikipedia.org/wiki/Instrument_landing_system#ILS_...

Cat III can be done with no DH, but you still require some RVR>0 (flare is done by the autoland system). Only IIIc could be done in theory with a blocked windscreen like in this case, but that's still not in standard operation anywhere that I know of.

Most jets have been capable of doing landing automatically for decades. This is allowed only on certified planes and runways and actually required for poor visibility situations. ILS CAT IIIc has no decision height or run way visibility requirements but no airport actually supports that yet. The main reason for this is that taxiing blind is kind of tricky. Landing and stopping the plane on the other hand is a solved problem. CAT IIIb landings are fully automatic.

The plane approaches, flares, and lands and keeps the plane on centerline (in some cases). Most (if not all) currently flying 737s are capable of this. The question is of course if this particular airport was ready for that (if not, I'm not sure if the autopilot would allow this) and whether the pilots were certified for this.

https://thepointsguy.com/guide/aircraft-operating-foggy-cond...

>I can’t help but think a blind landing is safer than depressurising a cabin full of passengers.

We're talking about 1000ft above Mexico city amount of altitude, here, not Mt. Everest. Any inherent risk from that is below the threshold of what's quantifiable. Skydivers routinely jump from 10,000ft.

Where they finally landed, Addis Ababa is at 7,726, Mexico City is 7,350.

That makes a lot more sense. When I initially read the article, I assumed they were landing at a typical runway within ~1000 feet of sea level and for some unfathomable reason decided to ascend many thousands of feet before opening the window. I forget how high Addis Ababa is!

In the remarks section: "IFR flt are not permitted to tkof fr Rwy 15 or apch and ldg on Rwy 33." So depending on the wind they might not had the option to land IFR.

You can circle to land if the approach is only one direction. Basically shoot the approach to minimums. Tower will say, circle to land north/south and you fly a normalish pattern, lower to the other end of the runway.

Circle to land requires visibility, you need to keep the runway in sight during the whole maneuver. So that wouldn't really have helped them in this situation.

It's one thing to land below minimums (as 0/0 certainly is) in the military, where you can very often be expected to do things with a low probability of survival.

It's another thing entirely to do it in a passenger airliner, and "depressurizing" at 8500' is nothing, you don't even need oxygen at all below 12,5 and even then only occasional usage for required crewmembers until 14,5.

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