The Great Ongoing Aviation Thread (general and other)

Miscellaneous and Personal Stuff I Must Share
2683

Sure. Sorta.

The equatorial bulge is a non-issue with airplanes. You’re swimming in the atmosphere and what really matters as to your maximum altitude performance is how much atmosphere is above you, not how much rock is below you.

Sounds counterintuitive, but it’s the atmosphere above you pushing down via gravity that supplies the air pressure you fly through. As you climb, that pressure reduces and eventually either your wing can’t generate enough lift in the rarified air to hold your weight, or your engines can’t generate enough power to push you fast enough to generate that lift or don’t have the excess thrust to push you any higher. When either or both of those things run out, you’re done climbing.

So that’s the theory. In practice you get other issues. It’s likely to be windy and turbulent around a craggy peak, especially that high in the overall atmosphere. Trying to clear a mountain by only 1000 feet is asking to get blown into it.

As the airflow flows uphill on the upwind side and also downhill on the downwind side, you’re going to have to transit that “hill” of moving air. If you already are near or at your max altitude (“service ceiling” in the argot), you’re going to have negligible excess performance to deal with that or even just turbulence that has no net motion, just choppy jumbling air.

Many, many lightplanes have met their doom this way against much lesser mountains. Usually when flown by somebody accustomed to flying over flat land who then tries to cross some mountains without knowing the hazards.

Just in terms of flight safety, ignoring legalities, I’d feel a lot happier crossing those mountains with about 5000 of clearance for turbulence and surprises, plus wanting another couple thousand above me to my service ceiling. Flying at service ceiling, completely absent mountains and turbulence, is already a lot like standing balancing on a beach ball. It’s awkward, precarious, ponderous, and unstable. Best to operate aways below that balancing beachball experience.

2684

Just to add to the excellent info that @LSLGuy posted, one might note that the earth’s oceans and atmosphere also bulge at the equator. In fact, though mostly due to the additional factor of convection at the tropics, the top of the troposphere is around three times higher in the tropics than at the poles. Thus if you had a plane with a 30,000’ service ceiling ASL you’d have a much greater margin of safety flying over Chimborazo than Everest. The distance of the mountain top from the earth’s center isn’t really relevant here.

2685

For that reason, when canyon flying I was taught to always approach mountain ridges at a 45 degree angle and with enough altitude to be able to turn back away if you encounter a strong leeward downdraft which can exceed the performance of thr plane.

This can cause you to run out of airspeed, altitude and ideas all at the same time.

2686

Of course, measuring from the centre of the Earth is non-standard. Measured from it’s base, Mauna Kea is the tallest mountain at about 13,800 feet.

2687

to spell it out further. the atmosphere will also bulge out at the equator

2688

Not General Aviation…

But still interesting.

2689

The video below suggests 1000 feet is enough separation. IANAPilot. Just tossing it out there (queued to where it is mentioned…no need to watch all of it for those who hate videos…the relevant bit is mentioned within seconds of where it is queued and then you can stop).

(NOTE: This is not a “gotcha”…this video was posted after my question and the responses to that question.)

2690

1 inch is enough separation to avoid disaster. The error is in planning for one inch.

Normal IFR terrain clearance minimums (at least in the US) are 1,000 feet in “non-mountainous” terrain and 2,000 in “mountainous”. I added the scare-quotes because those are magic FAA terminology that I don’t know the exact definition of. West Texas is non-, central Colorado is, but where is the cutoff? Heck if I know.

There was a near miss with a Chinese EVA Air 747 and Mt. Wilson near LAX a few years ago. They cleared the ridgeline by about 500 feet. After climbing in reaction to their ground proximity warning system.

Many years ago this happened:

The short version being the crew descended according to their understanding of their ATC clearance and flew into a mountainside.

Simplifying a bit … It later emerged that substantially the entire cadre of pilots in the USA had one understanding of the given clearance and the entire cadre of FAA ATC controllers had another due to mismatches in the FAA’s own procedural manuals. All the pilots thought they should descend immediately given that clearance, and all the controllers thought the pilots should stay at current altitude for a while longer when given the exact same clearance to descend commencing an approach! To this very day, every approach clearance given in the USA contains an extra clause to remove any opportunity for that particular ambiguity to occur.

The rest of the story is that while the rescue crews were working on recovering the TWA wreckage on that hillside in beastly weather they heard numerous other airliners invisibly roar overhead in the clouds at very low altitude. Some very, very low. Which was a large part of how the institutional misunderstanding came to light. TWA 514 was just the least lucky of the hundreds (thousands?) of jets that had done the same thing almost the same way day in and day out.

This accident was before any sort of ground proximity warning system had been invented. And in fact was part of the impetus to invent and deploy the first such systems. Which probably would not have saved them, but did save a heck of a lot of other airplanes later. The latest and greatest “Enhanced GPWS” is really, really nice and barring malfunction, would largely preclude such a thing happening today.

And yet EVA Air almost whacked Mt. Wilson.


Setting aside the accidents and almost-accidents, how much clearance is prudent / necessary depends a lot on the winds and weather. On a 100% calm day you don’t need to make allowances for turbulence and downdrafts near the ridgeline. As good as your eyeballs and altimetry are will be good enough.

Conversely, on a windy day crossing the ridge close to the highest terrain with the wind you may get beaten up pretty good by the turbulence, but unless the terrain on the other side is particularly unfortunately shaped you’ll probably make it. Flying the exact same altitude going the other way into the wind, you may well be shoved down into the still-rising rocks before you know it.

Given how rarely the wind is calm around ridgelines and mountain tops, planning to skim the terrain is (usually) planning to fail.

2691

I almost learned the hard way that high elevation points are good places to put towers. And towers under 500 feet don’t require strobes. Years ago I was flying low along the Ohio River to take pictures for a historical presentation. I kept the plane above the horizon of hills. I had a passenger watch for other planes while I took the shots. Everything was fine until I started talking about the view which naturally drew the attention of the passenger. When I looked up there was a tower that I was 5 seconds away from hitting. It was barely visible with the crappy blinking red light.

2692

Can a pilot listen to music or podcasts or watch videos while flying?

By this I mean while in the cruise phase of the flight. The plane is at its assigned max altitude, autopilot is on, nothing left for the pilot(s) to do until landing.

Can they do things to entertain themselves or must they always be monitoring the radio and instruments?

2693

Yes. You set it up so the radio or other microphones in the cabin overrides the music. That would be for personal aircraft.

2694

That’s its height above sea level, and also its prominence (height above surrounding terrain). This is far from the world’s best - Denali, for example, has over 20,000’ of both elevation and prominence.

But from its base on the ocean floor, Mauna Kea ranks as the tallest in the world: 33,500 ft, of which about 19,700 is under water.

2695

I’ve known pilots to setup a Bluetooth speaker and listen to music. I’m not a fan myself. If your aircraft has an ADF then you can tune in to AM radio stations. I used to listen in on late night flights around Australia. Pilots will often read magazines or a newspaper, things that don’t take your attention fully from the job.

Regardless of how much automation is engaged you still have a responsibility to monitor and even on longer flights there are position reports, frequency changes, weather avoidance etc.

2696

I wish I’d said that! :stuck_out_tongue:

2697

I had an intercom with a music input, but I never used it. I want to hear what the airplane is doing.

2698

Dad had ADF in his 172K. We’d listen to it sometimes on the long flights between WJF and MFR.

2699

Not GA, but this thread has a lot of side-tracks into non-GA mishaps …

Don’t know how much airplay this got outside of Miami since nobody was killed, but this was an interesting oops the other day at work.

Google News - Search. Some of the videos have some good detail.

The early thinking is a nose gear collapse during the landing roll led them off the side of the runway near the end. Unfortunately, they hit a radio shed and glide slope antenna with the right wing which duly opened up, spread fuel, and started a fire. Had they not hit that obstacle they’d probably have come to a halt in mostly one piece with no fire. It seems both main gear sheared off at some point, probably when they dropped into the muddy grass. They’re designed to break off cleanly when overloaded aftwards like that and from what little I can see it appears they did as designed.

The bad luck for the rest of us is they came to a halt blocking 2 of the 4 runways at MIA. And of course during the initial fire/rescue event the whole airport is closed to all takeoffs & landings until the disaster is contained.


At the moment this happened I was flying back from Saint Thomas along with a couple dozen other jets all droning up the Caribbean and Bahama islands chains towards MIA on a sunny warm thunderstorm-free afternoon. Life is good. Boring, but good. Once back at MIA I’ll drive home for a well-deserved couple days at home.

Then ATC says “OK everybody, listen up. … Miami is closed for a mishap. That’s all we’ve been told. Everybody plan to hold. Instructions to follow.”

Cue mad flail in 40-50 cockpits over the Atlantic, the Gulf, and all up & down Florida as we all start doing our contingency planning. With no real idea yet how bad the mishap was, how soon (or whether) MIA will reopen, what their re-opened arrival rate will be, etc. Nor exactly how many other jets are headed there, where else we individually can go that won’t itself be overwhelmed with traffic, both normal and diverted.

Also cue mad flail at ATC as they dust off their playbook for stopping the flow of jets on a dozen converging routes aimed at MIA from all points of the compass. Of course the jets don’t stop, so they each need their own separate block of sky and altitude to circle in while making no progress towards MIA.

We all always have a hip-pocket plan. Which will fail for most of us when 50 jets all try the same plan at the same time. Of course the longer you circle, the fewer your options become as your remaining range inexorably decreases. And as the folks tighter on fuel, or more antsy, than you are bail out and start clogging the other airports too.

ATC of course has their playbook and pretty quickly their hardest job is simply transmitting all the instructions to all the airplanes fast enough with no mistakes at either end.

In the event we and a half-dozen others circled over Nassau, Bahamas for about 25 minutes. Meanwhile many others were circling either closer in or 100 miles farther out circling someplace else. A well-practiced drill, but still a increased workload and increased opportunity for a screw up.

Then MIA reopened with a reduced arrival rate. We and most others drove on in and landed only a little lighter on fuel than desirable, though a bunch lighter than normal. But had our delay lasted another 5 minutes we’d have been diverting, wasting a couple hours getting back to MIA, and perhaps joining a real horde of diverting jets and the ensuing madhouse on the ground wherever we would have gone. From the radio chatter, only a couple non-airline folks near us diverted, but lots of airliners, including us, had told ATC we could not wait much longer when the logjam broke.

So much for boring.

Once on the ground it happened that the taxi route to our gate afforded a view of the MD82 sitting on its belly in the grass surrounded by a couple fire/rescue vehicles and a horde of pickup trucks. We could only see the left side which was unburnt. Which was the first we knew of who did what how bad. Presumably the passengers and FA’s had been glued to Google news on the Wi-Fi for the last 30 minutes and had all already seen the whole accident replayed a dozen times. We were busy.

Now 48 hours later it appears they’ll get the wreckage hauled away today / tonight and be able to start repairing the gouges in the concrete, repainting stripes, and replacing damaged signs, radio equipment etc. So MIA ought to be back to normal ops tempo in another 24-48 hours, though some stuff won’t be fully fixed for weeks.


I hate it when that happens.

2700

I would think a collapsed nose gear still gives you differential braking so it’s 1 of 2 things, one of the thrust reversers didn’t deploy or a brake locked up. I worked for a company that had a DC-8 with a thrust reverser issue and it did the same thing. They managed to hit everything located next to the runway and just grind the plane up.

I once blew a tire on a small plane (it didn’t have separate brakes) . It absolutely dragged the plane off the runway. I finally had to give up and steer it further off the runway to avoid hitting a light. That was at 70 mph in a little plane. Landing over 100 with the weight of a MD-82 is a lot of energy to dissipate.

2701

Agree with a simple nose strut failure / collapse they should have had differential braking. But the nose strut failing could have torn open both hydraulic systems, which would quickly have led to almost main wheel braking at all; just one good shot with the hydraulic accumulators.

There are accident pix which show both reversers deployed, so that’s not it. The MD-80 also has a very long nose to main-gear distance. So once the airplane got a little bit sideways to its motion vector, the extra drag from the nose dragging on the runway has a very long lever arm to try to spin the airplane around until it’s sliding backwards. Maybe with more turning force than the differential braking can muster.

The best vid I saw of the last few seconds in motion the airplane’s track was about 45 degrees off its heading, sliding right side forwards towards its own 1-1:30 clock position. IOW their heading was diverging CCW from their track. That was just before the right wing struck the ground obstacles which really slowed them down and slewed them around the other way (clockwise).

2702

More on the perennial question: