Lufthansa used to have a flight in the 1980s I think (maybe early 1990s as well) that routed Frankfurt-San Juan-Bogota-Lima-La Paz, using 747-200s.

Were the aircraft modified to deal with cabin altitude issues at such high altitude? La Paz is located at over 13'000 feet. I heard there had been aircraft types where the oxygen masks dropped from the cabin ceiling when doors opened at La Paz airport.

Are later versions of the 747, i.e. 747-400 and 747-8, capable of operating to La Paz without issues or modifications? How do they deal with the cabin pressure issue?

mozart wrote:

Lufthansa used to have a flight in the 1980s I think (maybe early 1990s as well) that routed Frankfurt-San Juan-Bogota-Lima-La Paz, using 747-200s.

Were the aircraft modified to deal with cabin altitude issues at such high altitude? La Paz is located at over 13'000 feet. I heard there had been aircraft types where the oxygen masks dropped from the cabin ceiling when doors opened at La Paz airport.

Are later versions of the 747, i.e. 747-400 and 747-8, capable of operating to La Paz without issues or modifications? How do they deal with the cabin pressure issue?

Sounds like folklore. The aircraft pressurization system wouldn't be active after shutdown. Why would the oxygen masks drop?

TTailedTiger wrote:

Sounds like folklore. The aircraft pressurization system wouldn't be active after shutdown. Why would the oxygen masks drop?

Passenger masks deploy on lots of types when cabin altitude exceeds 14,000 ft.

Aircraft (tail number) can be outfitted and certified to be used at high altitude airports. Usually there is a possibility to deactivate the automatic deployment of the passenger oxygen mask or raise the threshold for the activation. This is incorporated in a special procedure for flying into these airports. Special crew raining is required as well.
I am sure boeing offered some kind of this systems on the B747. Airbus offers it for most of their models. Thats what Lufthansa did.

Irrespective Oxygens masks, won’t there be a cabin pressure alert in the cockpit already during approach/landing? Crews set altitude of the landing field, and then cabin pressure adjusts to that. But if that cabin pressure is 13’000 feet, won’t that trigger an alert?

China has 4 airports above 14000ft. Airbus created a mod for A320’s that operated to these places. It placed a switch in the cockpit which deactivated the auto mask drop during the approach.

FCOM states:

HI ALT LANDING pb-sw
This pushbutton-switch changes the altitude threshold for the deployment of the passenger oxygen masks.
OFF :
The masks drop, if the cabin pressure exceeds 14 000 ft (+250, -750 ft).
ON :
The masks drop, if the cabin pressure exceeds 16 000 ft (+250, -750 ft).

How does one do a QFE approach at an airport such as La Paz? Aircraft I’ve flown wouldn’t allow an altimeter setting that low.

In mid-1970s flew into LaPaz on an Aerolineas Argentinas 707 and immediately upon landing all the oxygen masks dropped from the overhead rack. That rea;;y freaked me out!

GalaxyFlyer wrote:

mozart wrote:

Irrespective Oxygens masks, won’t there be a cabin pressure alert in the cockpit already during approach/landing? Crews set altitude of the landing field, and then cabin pressure adjusts to that. But if that cabin pressure is 13’000 feet, won’t that trigger an alert?

There’s a high altitude airport mode when the high elevation airport is loaded into the FMS as destination or origin. All automatic in the planes I flew.

I’m guessing the cabin altitude is scheduled as normal for whatever cruise level is reached then slowly ascends to ‘meet’ the aircraft at the touchdown zone elevation?

On take off from a very high altitude airport (significantly above the height that the cabin is normally at) what is the process for bringing the cabin up to that normal pressure? Is it done immediately after engine start? Does it put pressure on the packs and thus you don't want it during a high altitude take off?

GalaxyFlyer wrote:

No, it begins after lift-off, aside from normal small pressure, 0.125 PSID, IIRC, on taxi. The cabin descends to the normal scheduled altitude for the flight. If going from Quito to Guayaquil, it’d start right down toward sea level as it’s a short flight. If Quito to MIA, it’d descend to normal cabin for the flight level, then descend to meet the plane at sea level.

Very interesting, thank you. That answers a lot of my initial questions.

What I’d like to find out is what is done on 747s when they operate(d) out of La Paz?

When approaching, the system sets the cabin pressure to the altitude of the landing field, in this case >13,000ft. This should trigger an alarm, right? Then what? The alarm simply gets cancelled? Or is anything else done?

For taxi and takeoff - if I understand the above post correctly, one lets the system in automatic mode, the only manipulation is the “target pressure”, correct? Where is that set on the B747?

Thanks, Chris


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mozart wrote:

GalaxyFlyer wrote:

No, it begins after lift-off, aside from normal small pressure, 0.125 PSID, IIRC, on taxi. The cabin descends to the normal scheduled altitude for the flight. If going from Quito to Guayaquil, it’d start right down toward sea level as it’s a short flight. If Quito to MIA, it’d descend to normal cabin for the flight level, then descend to meet the plane at sea level.

Very interesting, thank you. That answers a lot of my initial questions.

What I’d like to find out is what is done on 747s when they operate(d) out of La Paz?

When approaching, the system sets the cabin pressure to the altitude of the landing field, in this case >13,000ft. This should trigger an alarm, right? Then what? The alarm simply gets cancelled? Or is anything else done?

For taxi and takeoff - if I understand the above post correctly, one lets the system in automatic mode, the only manipulation is the “target pressure”, correct? Where is that set on the B747?

Thanks, Chris


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The alarm can be set to a higher altitude with a mod, so it doesn't go off.


IIRC on the 747 target is set by FMS.

LH used to fly many decades into LPB, they had routings with B707, later with DC10 FRA NYC LIM LPB SCL and returned same route, it was later changed to FRA SJU BOG LIM LPB with 742 service, which also had the FRA CCS LIM LPB routing. I flew the route many, many times, and never had a single incidence regarding any tech or O2 masks falling.
In fact - well, I live in Bolivia - I have never had any O2 falling masks incidence landing LPB, or in fact, anywhere in Bolivia.
I am not a pilot nor engineer, nor technical expert, but I understand this is what they do when landing @LPB: Pilots from foreign airlines (in the past, LH, AA) donned Oxygen masks for landing and takeoff operations - but pax were safe and sound in the back, knowing the crew knew and knows what to do.