The Great Ongoing General Aviation Thread

It’s the radar altimeter. It’s a simple but very important device that looks down and measures the distance from the antenna to the ground or whatever obstacle happens to be below it. it doesn’t need to know anything about obstacles in the area, it just measures what it sees. The display from the radar altimeter (radalt) is typically displayed on the flight instruments below 2500’. The callouts themselves are an option for the EGPWS, Enhanced Ground Proximity Warning System, but they just work off the radalt. It’s not unusual to get a “ONE THOUSAND” call going over a hill on approach, then another “ONE THOUSAND” call when you are again at 1,000’ over flatter ground. It is normally setup for calls every ten feet from fifty to the ground, other calls are more variable and just depend on which ones the company wants to include.

GPS altitude is available in the cockpit but not used for anything obvious that I’m aware of. You are correct that GPS altitude is not accurate or responsive enough for landing callouts.

The EGPWS does have obstacles and terrain in its database, but this is not used for the advisory callouts, it is used for ground collision warnings.

As for GPS approaches, GPS just by itself is not as good as an ILS approach, but there are supplementary systems that make it pretty good.

The problem with GPS is that it may be accurate to a few feet on one day, or fifty days, but on another day it might not be, and there’s no way to know, just using pure GPS, whether you’ve got a good day or a bad day. So GPS approaches have to be designed with the bad days in mind. A bad day is not one where you can’t get enough satellites, or some satellites are faulty, the GPS receiver can give warnings about that. The bad days are where everything is working perfectly normally but the errors all happen to cumulate in one direction and so instead of being a few feet from your expected position, you’re actually 100 feet from it.

To combat the above issues, there are augmentation systems available which basically work out the local GPS position error and then broadcast it to all GPS receivers in range so they can compensate their computed position. An example would be a ground station that knows its own position exactly, and knows what GPS thinks its position is in real time, and can then broadcast that error value.

The advantage of an ILS is that it is physically located at the end of the runway and projects a physical radio beam out along the approach path. It is very precise horizontally and vertically and gets more precise the closer you get to the runway. There are still traps with an ILS but an ILS will never put you 100’ off to the side of the runway.

Richard - might be a good place to explain ILS outer and inner markers.

A Scandinavian tragedy:

It went straight in and was caught on camera..

Guess i will post this here. Richard Branson plans to fly this Sunday. Bezos is all “nuh-ah, not space” (meanwhile Musk is thinking neither of these jokers have done 1/10 [1/50?] of what SpaceX has done)
Might be worth watching in any case


New Shepard and Virgin Galactic were so exciting a decade ago, but now both of them look almost like toys compared to what SpaceX is doing. Suborbital tourist flight is a technological dead end, and not particularly exciting after watching Starships fly.

Besos comes off looking seriously petty on this.

I got to thinking about what you said. I’m not sure it was a technological dead end. The concept of launching satellites from a plane seems like an extension of their efforts with Orbital ATK , Virgin Orbit, and Scaled Composites Stratolaunch

I said that suborbital human flight was a technological dead-end, not smallsat orbital launches (which Blue Origin does not do).

You can definitely launch small sats from the air. The Pegasus rocket has been doing it for decades. And Virgin Orbit is doing it. The problem is that when such systems were envisioned, they were attempting to compete against old school rockets which could cost $10,000-$50,000 per kilo to LEO. Launch costs have declined dramatically since then, and the small sat business is very competitive.

Take Virgin Orbit’s LauncherOne. Dropped from its plane it can carry 300 kilos into Low Earth Orbit for an estimated $12 million dollars. That may have made sense when alternatives could cost $200 million or more per launch.

But SpaceX, for example, has a rideshare program for small sats. A falcon flight costs about $60 million, and can carry 22,000 kgs to LEO. A single mission can carry a lot of smallsats.

You can use their pricing calculator here:

According to that site, I can buy a 300kg ride share for 1.2 million. Virgin Orbit can’t come close to that price - it’s 1/10 the cost of one of their launches.

They also face heavy competition from more modern platforms like the Electron, a 3D printed rocket with electric turbopumps.

Bezos’ New Shepard is a technological dead end. We have solved powered rocket landings, and their small engine isn’t useful for orbital flight. Virgin Orbit’s air launcher is a 30 year old concept, and the plane design is two decades old. Both companies just advanced so slowly that technology passed them by on the way to the launch pad.

And if Starship works, costs will drop even more. And Electron is building newer, bigger, fully reusable 3D printed rocket. This kind of stuff is exciting. Another air launched smallsat launcher, not so much. I suspect it may find niches, such as rapid turnaround launches for the military, but that’s about it.

Yes but my point was that the dead-end technologies led to plane launched satellites.

I remember years ago arguing with engineers who told me launching a rocket from a plane didn’t gain anything because it’s all about escape velocity. Math ensued, my eyes glazed over and I walked away thinking it wasn’t possible.

Worked for ASAT

Those guys were wrong. A rocket uses a substantial portion of its fuel just clearing the lower atmosphere. Hell, a Saturn 5 used 4% of its total fuel just clearing the tower. The rocket equation is an exponential, so if you can avoid those first fuel-gobbling minutes and start the rocket at high altitude where drag is low and 500 mph, it can be a big win. As much as the equivalent of a 22% increase in delta-V.

The problem is that you can only launch small rockets this way, and small rockets already suffer from poor TWR because their structures are proportionally heavier. And the cost savings are hard to realize because of the need for an expensive launch plane, and the operational costs around the whole aystem. It’s at best a niche launch method with some specific advantages formspecial cases.

For example, you can launch to any orbital inclination easily, and short time-frame scheduling may be easier. The latter is less useful now given the rapid cadence SpaceX is maintaining. It used to be that if you needed a launch you might have to wait years before a berth was available. Air launchers could have helped there. But again, they took so long to bring that system to market that the need for it has been greatly diminished.

No, they really didn’t. Plane launched rockets showed up long before New Shepard, and the BE-3 wngine it uses is a pretty standard Hydrolox engine that isn’t powerful enough to take a rocket to orbit. It MAY wind up as the precursor design to a new second-stage engine, but there are already lots of candidate engines for those roles out there, and Blue Origin’s big engine, the BE-4, shares nothing in common with it. It’s a Methalox engine, for starters.

But do they have to have substantially heavier structures? If a rocket is using internal pressure to keep it’s shape then wouldn’t an exoskeleton “sling” work to suspend it from a plane? The sling releases and falls away.

The bigger the rocket, the smaller the percentage of weight due to the structure. For example, the skin will be roughly the same thickness on both, but the square/cubed relationship of area to volume makes it weigh proportionally less.

That’s a main reason why Starship had to be so large, and why SpaceX can’t reuse the second stage of Falcon 9. You need a huge rocket before the math on full reusability works out.

Can a person open a door on a commercial plane while in flight?

My understanding is the pressurized plane exerts waaaaay more force on the doors than a human could ever overcome. The doors open inward and the pressurized plane is pushing outward and the forces are well beyond human capacity to overcome.

That said, I can understand it is unsettling for passengers to see someone working diligently to open a door to the outside in flight and crash the plane and that the passenger needed to be restrained (for many reasons).

She was duct taped to her seat (including her mouth) because she was biting and spitting on the crew. The passenger who thought it could be handled better should post a solution.

Celebrating what would’ve been a great American aviator’s 100th birthday this weekend:

I had no idea this was a thing:

Not General Aviation, but…

British Airways jet took a nose dive because mechanic was too short to lock landing gear (