Ask The Pilot

[jb747]

I guess the answer is to never trust anyone who agrees with you.

 

[mjt57]

I guess the answer is to never trust anyone who agrees with you.

Sorry, that's wrong....

 

[Quickstatus]

Why didn't Boeing use Chemical O2 generators in the B747-100-400 for passengers?

I understand the 737 had a hybrid oxygen system
- oxygen tanks for flight crew and chemical generators for passengers

 

[exLXCXFF]

This is a scary one: Accident: Vietnam B789 at Munich on Aug 15th 2026, late rotation, tailstrike, runway overrun, tyre damage

 

[AuSammy]

This is a scary one: Accident: Vietnam B789 at Munich on Aug 15th 2026, late rotation, tailstrike, runway overrun, tyre damage

To an untrained eye looks like tyre damage least of their issues (and probably caused from hitting lighting arrays) beyond end of runway)

 

[jb747]

Why didn't Boeing use Chemical O2 generators in the B747-100-400 for passengers?

I understand the 737 had a hybrid oxygen system
- oxygen tanks for flight crew and chemical generators for passengers

Hybrid systems are probably the most common. As far as I know, all crew system are pressurised gas, presumably because at very high altitude it actually needs to go to the mask under substantial pressure. Called pressure breathing, and it's extremely uncomfortable.

But back to the base question, it would be a question of duration. Chemical systems give up to around 18 minutes, where the pressurised systems can be measured in hours. There are many cases where going to 10,000' isn't possible due to terrain, so the initial descent could be constrained to as high as 20,000'. You can also come up with examples where, due to range issues, you can't cruise at 10,000'. Being able to stop at a higher level (in the order of 15,000-20,000') could make the difference between getting to an airfield, or going for a swim.

 

[jb747]

This is a scary one: Accident: Vietnam B789 at Munich on Aug 15th 2026, late rotation, tailstrike, runway overrun, tyre damage

To an untrained eye looks like tyre damage least of their issues (and probably caused from hitting lighting arrays) beyond end of runway)

The far end of the runway tends to be an unfriendly place, and best not visited. There are no clues in the video. Configuration looks ok. There doesn't appear to be any elevator input until right at the end, so perhaps they were having a sleep.

 

[Brissy1]

I guess the answer is to never trust anyone who agrees with you.

Agree

 

[747sp]

With the Vietnam 789 flight in Munich there is different speculation to the cause.
Some people think the brakes may have been on .
I was wondering what controls are in place to avoid having the plane accelerating at the same time it is braking.?
On the same theme can you abort a landing once the brakes have been fully applied?

 

[jb747]

The issue is not that all the brakes were applied, as they would be if a pilot used his foot brake pedals, or had applied the parking brake. The suspicion is that one of the four bogie pairs had braking applied, so two sets of brakes, across one wheel pair. That’s a quarter of the total braking capacity. I doubt that it ever would have gotten airborne if they had been applied for the entire roll, nor would the tyres have survived that long. The images of the skid marks show very active ABS, but not the sort of shape you’d expect if the tyres had failed. I don’t know the 787 braking system, but supposedly it’s completely electrically operated. TBA at the moment.

Most commonly, this sort of event is the result of inaccurate load figures, or incorrect take off data calculation. If the brakes are involved, and it seems a big if, then it would possibly be a first.

 

[RooFlyer]

@jb747 , Juan Browne discusses the electrical brakes in a clip I posted here, if you are interested.

 

[jb747]

A theory I heard today, from Mover on YT, and which makes some sense basically says that they got the performance data wrong (for whatever reason), but at the end of the runway one pilot was going, and the other has jumped on the brakes. If that's even close, they they're very lucky to have come away as well as they did.

 

[mjt57]

A theory I heard today, from Mover on YT,

Do runways have markers that show how much of it is left (like racetrack braking markers)?

Given that these pilots would've done many MTOW departures I'm surprised that they didn't notice something early on. "Eh, Bob, shouldn't we be doing 80 kts by now?"

off topic but Mover has a video coming out soon why he chose to quit AA (he was on 787s). That should be an interesting one. Like he said, "people probably think that I'm crazy to give up a $300k job".

 

[Rabs97]

Do runways have markers that show how much of it is left (like racetrack braking markers)?

The touchdown zone markings for the opposite threshold give an indication the end of the runway is coming up fast.

 

[jb747]

Do runways have markers that show how much of it is left (like racetrack braking markers)?

No. Military runways do, but I don't think they're all that useful.

Given that these pilots would've done many MTOW departures I'm surprised that they didn't notice something early on. "Eh, Bob, shouldn't we be doing 80 kts by now?"

That's what you'd expect, so it will be interesting when we eventually see the experience levels of the crew.

But, one of the things that has changed over the last 20 years or so, is how crews work out their take off data. When it was done manually, it was quite complex, and for that reason, was generally confined to only a single configuration. If memory serves correctly, we used Flap 20 for 99% of takeoffs in the 747. Also, it was decreed that take off power would never be less than the climb power that you were using...so there would always be a power reduction at clean up, never an addition. But, as laptops/ipads and their ilk became prevalent, the performance data was calculated on them. They were powerful and flexible, and so could handle multiple flap, pack, or APU, configurations. As management's aim was always lowest wear/cost, the use of very flexible configurations became the norm. Use of takeoff power less than climb also became common. The result of this was a disconnect between the pilots and the aircraft performance. As the configuration you use is never the same there becomes no normal. A very slight change in anything (wind, weight, temp) could result in completely different configuration, and power setting.

off topic but Mover has a video coming out soon why he chose to quit AA (he was on 787s). That should be an interesting one. Like he said, "people probably think that I'm crazy to give up a $300k job".

I'll be interested to see it, but I get the feeling that he wasn't in love with the airline career, irrespective of the pay. And he appears to have an alternative income, so with that comes options. FO on a 787 is nice, but for a command I guess he'd be back to something much smaller and US domestic. That's not all that attractive....