TutiFruiti
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Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 1:28 pm

Hello All.

I happen to video a plane under plane by chance but two important questions still in my mind , as i could not find answer.

The video is as follows

https://www.youtube.com/watch?v=oNGI8fX71fM


1) Does a plane passes under another plane fully below & parallel vertically it or it is bit to the side under the the upper plane..?

2)In this video, it a 'pure' plane under plane or the plane passing under is coming at an angle or its to the side?.. as stated in above? From 13 to 17 seconds, the camera focus on winglet of upper plane to give a sense of direction. In the end of video, the lower plane seems to get under the upper plane!!

Hopefully, the questions stated are understandable.

* The upper plane is 737-900ER and lower looks like 747

Is it possible to guess from such video what might be the case ?
 
747Whale
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 2:18 pm

From the video, it appears there are several thousand feet separation between the aircraft. They may pass in any direction, travel in the same direction, etc.

It appears that the aircraft approach from converging angles; the 737 is approaching from the 747's left, and the the 747 overtaking from the 737's right. It may be that they pass one under the other. The parallax and frame of reference against the mountains below certainly appears to support that the paths of the aircraft drift together and pass, the 747 under the 737.

It's no cause for concern.
 
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Starlionblue
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 3:43 pm

Planes pass under and over other planes all the time, at various angles, with separations as low as 1000 feet vertically. If we are crossing head on, we can often hear the other aircraft as it passes.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
TutiFruiti
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 5:13 pm

Thanks 747Whale and Starlionblue ... It drift together and pass..agree...!!
also..
i guess, after Emirates A380 almost made Glex fell out of sky on Arabian Sea near gulf of Oman..the Big Aircrafts like 747-8, A380s and also the 757 (wake in relation to size), may be kept more apart these days..
 
747Whale
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 6:31 pm

In-trail separation depends on the airspace, but is well established with air traffic control. There are many parts of the world, however, in which separation isn't by radar, but by position reporting and time, and in many places vertical separation is 1,000 at all altitudes (used to be 2,000' in what is now "RVSM" airspace (reduced vertical separation minima). The old 2,000' spacing was reduced to 1,000' and phased in around the world over several years, allowing more traffic at the higher flight levels at 28,000' and above. This system is called RVSM, and is fairly universal now.

Because traffic is stacked 1,000 apart vertically, in certain cases the in-trail separation, or in other words the distance between one aircraft following another), is established. Some aircraft with the potential for greater wake turbulence are called "heavy," in certain areas, to distinguish their greater weight and greater potential for upset. The. Boeing 757, while not a true "heavy," is also included in that category for wake purposes, because it has shown to generate a greater than normal wake vortice.

A "jet upset" can occur at altitude through a wake turbulence encounter, or for other causes, including certain cases of clear air turbulence, convective activity (thunderstorm), instrument malfunction, runaway autopilot or trim, etc. These cases are recoverable, but cause a deviation from the intended flight path.

On long oceanic legs, it's common to apply "SLOP," or strategic lateral offset procedure, which is simply flying 1 or two miles to the right of course. As navigation has become so precise, often placing aircraft on the same track or airway exactly over one another, the use of SLOP builds some randomness into the routing, meaning that it moves aircraft apart laterally so that they're not right on top of one another.

On occasion on oceanic routes, I've had a radio altimeter indication in cruise when overtaking another aircraft on the route; the other airplane is 1,000' below, and I'll get an indication of 1,000' and a voice from the enhanced ground proximity warning system (EGPWS).

Wake turbulence encounters and jet upsets do happen, though they're a rarity. There are occasions enroute when I do detect a wake encounter, often with the tell-tale lateral movement of the airplane or a slight tugging rolling motion

I fly a widebody airplane and am often the one generating the wake, but I've encountered them many times. Even small airplanes put out wake turbulence, primarily from wingtip vortices, which are spinning cones or horizontal columns of air that are created at the wingtips of most aircraft. One of the jobs I do involves flying a single engine turboprop loaded about 25% over the original published gross weight, in formation with other aircraft, close to the ground. Even behind a light twin like a King Air 90 or 200, the wake turbulence can be very noticeable and can become dangerous if one remains in the descending wake. It's something any glider pilot instantly understands from being towed.

Passing above or below other aircraft enroute is very common, and very, very seldom any kind of problem.
 
WPvsMW
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 7:32 pm

747Whale... your classrooms must be some of the best, based on how well organized and written your "instructor" posts are. Thanks. There are lots of "student lurkers" on a.net, most of whose IRL instructors have a small fraction of your experience.

Cropdusting in formation! Sounds like Warthogs in Desert Storm.
 
BoeingGuy
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 7:45 pm

747Whale wrote:
On occasion on oceanic routes, I've had a radio altimeter indication in cruise when overtaking another aircraft on the route; the other airplane is 1,000' below, and I'll get an indication of 1,000' and a voice from the enhanced ground proximity warning system (EGPWS).



EGPWS has something called "overflight protection" that is logic designed to prevent the Mode 6 Altitude Callout (e.g. "ONE THOUSAND") and a nuisance TAWS alert (e.g. "TOO LOW TERRAIN") when there is a momentary radio altitude input due to overflying another airplane. It's sees that the radio altimeter input instantaneous went from NCD to say 1000, not ramping up normally as would be expected when actually close to terrain, so inhibits the EGPWS functions.

I'm perplexed why you would hear the 1000 feet callout since it's designed not to do so. I'm speculating maybe the airplane had older version of EPGWS that didn't have the overflight logic, although I don't know when this logic was developed. The Display system doesn't have such logic so seeing that Radio Altitude pop up on the PFD is expected.
Last edited by BoeingGuy on Mon Jan 07, 2019 7:48 pm, edited 2 times in total.
 
747Whale
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 7:46 pm

That wasn't crop dusting, actually; it was firefighting in a single engine air tanker (SEAT). The biggest problem with being heavy (12,500 lb airplane, but flown at 16,000 lbs) is that at the high density-altitude mountain locations in winds with downdrafts, behind the leadplane the tanker can get in the wake and be forced down the to ground. When already close to the ground (such as turning inside a canyon), there may be nowhere to roll out of it or to escape, so prudent positioning can be quite important.

When I was eighteen, we did a lot of formation spraying. Today there's GPS, but it wasn't available then, and marking a row on a field was done either with a flagger (a guy holding a flag on a stick, who waved the flag and gave us an aiming point as we flew across the field...who moved a wingspan upwind with each pass), or an "automatic flagman," which is a long box that sits atop the wing, and dispenses a streamer with a press of a button or trigger in the cockpit. The idea is that when leaving the field after a pass, one fires off a streamer from the automatic flagman, and upon turning around for the next pass, spaces upwind off the streamer. It's a marker. On calm mornings, smoke can be used, too, if it won't be drifted off the last pass. Spacing in ag work is very critical, because any gaps in the coverage on the crop will turn up as "skips," or areas of weeds or contamination, and also because of chemical drift.

Because of the expense of flags (and the litter aspect, though they're biodegradable), we often sprayed in formation. If the spacing and timing is right, one airplane can be entering the field as another is about to pull out, and they work off each other. In a tight formation, it's easy to get really solid coverage on the field, and we did a lot of that. Spray work also involves flight under powerlines at times, in order to get coverage right to the edges of the field; it's sometimes safer going under than trying to judge going over, especially with different combinations of wires. Consequently there were times when we flew formation under powerlines. (and I've ben with guys a few times when, unfortunately, it became through powerlines).

BoeingGuy wrote:
I'm perplexed why you heard the 1000 feet callout.


We were, too.

Yes, it was EGPWS.
 
BoeingGuy
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 8:49 pm

747Whale wrote:

BoeingGuy wrote:
I'm perplexed why you heard the 1000 feet callout.


We were, too.

Yes, it was EGPWS.


I know it was EGPWS. ;) Every Boeing model, except the KC-46, has been delivered with Honewell EGPWS for over 20 years. (They all had GPWS before that when look-ahead terrain was developed). The KC-46 has T3CAS made by ACSS, as do a number of customers like AM who have retrofitted their Boeing fleet with T3CAS after delivery. The two Ground Prox System systems are very similar of course.

My point was that I'm especially perplexed why you heard that callout in cruise considering the box is specifically designed not to do that.
 
747Whale
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Re: Plane passing under Plane question? 747 from 737

Mon Jan 07, 2019 11:15 pm

BoeingGuy wrote:

I know it was EGPWS. ;) Every Boeing model, except the KC-46, has been delivered with Honewell EGPWS for over 20 years.


This Boeing model was designed and delivered a bit before that time frame. 1969. Don't recall the delivery date, but long before the last 20 years.

It had EGPWS. It wasn't delivered with it. Like many aircraft.

BoeingGuy wrote:
My point was that I'm especially perplexed why you heard that callout in cruise considering the box is specifically designed not to do that.


As were we.
 
TutiFruiti
Topic Author
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Re: Plane passing under Plane question? 747 from 737

Tue Jan 08, 2019 9:24 pm

747Whale wrote:
BoeingGuy wrote:

I know it was EGPWS. ;) Every Boeing model, except the KC-46, has been delivered with Honewell EGPWS for over 20 years.


This Boeing model was designed and delivered a bit before that time frame. 1969. Don't recall the delivery date, but long before the last 20 years.

It had EGPWS. It wasn't delivered with it. Like many aircraft.

BoeingGuy wrote:
My point was that I'm especially perplexed why you heard that callout in cruise considering the box is specifically designed not to do that.


As were we.


Guys.. you are way too expert... I am still absorbing or trying to absorb all the stuff mentioned above :stirthepot:


'''On occasion on oceanic routes, I've had a radio altimeter indication in cruise when overtaking another aircraft on the route; the other airplane is 1,000' below, and I'll get an indication of 1,000' and a voice from the enhanced ground proximity warning system (EGPWS). ''''

wow.. thats something totally new.. That at cruise a EGPWS warning can momentarily sound thinking that the aircraft passing right underneath is 'ground'..

btw.. Old Boeing, MD, Tristar alert sounds are awsome and scary in right way..

Airbus alert sounds dont send the sense of intensity of problem faced. Kind of very relaxed and nice sound even though aircraft might be in real danger..!!
 
stratclub
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Re: Plane passing under Plane question? 747 from 737

Tue Jan 08, 2019 9:44 pm

Huh? What are you talking about? I'm completely baffled. It is true that modern aircraft have an audible warning if some one violates your airspace. What is so strange about that?
 
BoeingGuy
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Re: Plane passing under Plane question? 747 from 737

Tue Jan 08, 2019 10:04 pm

stratclub wrote:
Huh? What are you talking about? I'm completely baffled. It is true that modern aircraft have an audible warning if some one violates your airspace. What is so strange about that?


Again, it's not designed to do that. I've mentioned this at least twice now. The EGPWS has specific logic that is designed to inhibit giving the Altitude Callout (e.g. "ONE THOUSAND") and/or a GPWS alert (e.g. TOO LOW TERRAIN) when one airplane passes over another at cruise altitudes.

What you stated is completely false. Modern airplanes do not have an audible warning if someone "violates" your airspace. Passing over another airplane in a legal altitude in RVSM airplane is not a "violation". It's not strange because it's not correct. The exception of course is if TCAS calculates unsafe separation.

It is neither desirable or correct to gave an Altitude Callout when an airplane passes 1000 feet over another in RVSM airspace. Doing so would likely be deemed a non-compliance to CFR 25.1301, CFR 25.1309 and possibly CFR 25.1302.

I'm speculating that the installation that 747Whale describes is an older STC installation of an older version of EGPWS designed for 747 Classics that didn't have the "overflight protection" logic. That's why he heard that 1000 callout. That is not consistent with current EGPWS design.

Modern Boeing airplanes will not give an Altitude Callout or GPWS alert when passing over another airplane. That is by design. Period.
 
747Whale
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Re: Plane passing under Plane question? 747 from 737

Wed Jan 09, 2019 8:47 am

TutiFruiti wrote:
wow.. thats something totally new.. That at cruise a EGPWS warning can momentarily sound thinking that the aircraft passing right underneath is 'ground'..


Yes and no: the EGPWS doesn't really think anything; it's designed as a warning system if the flight encroaches on half a dozen different predesigned envelopes; proximity to the terrain is one of them. Closure rate, descent rate and other factors also provide warnings, and annunciations are given during a normal approach, too.

The pilot sees a radio altitude indication on a display, as well, and it doesn't "know" if it's ground or something else; it's height above what's directly beneath the aircraft. This information comes from a "radio altimeter," sometimes called a "radar altimeter." If there's something down there to "bounce" a signal from, whether it's ground or an aircraft, the display will momentarily indicate it. It's not supposed to have an accompanying announcement of "one thousand feet," however: that should only be made when approaching to land (as opposed to cruise, or taking off). In our case, we shouldn't have received an annunciation in flight; only an indication on the display.

TutiFruiti wrote:
btw.. Old Boeing, MD, Tristar alert sounds are awsome and scary in right way..


Depends on the alert, but the main alert on the MD sounded to me like a bad gameshow...kind of fruity. They call it a "tri-tone" due to three chimes, but I laughed the first time I heard it. More like something that belongs on an ice cream truck.

BoeingGuy wrote:
What you stated is completely false. Modern airplanes do not have an audible warning if someone "violates" your airspace. Passing over another airplane in a legal altitude in RVSM airplane is not a "violation". It's not strange because it's not correct. The exception of course is if TCAS calculates unsafe separation.


I think he's actually referring to a TCAS traffic advisory (TA) or resolution advisory (RA). That could be interpreted roughly as another aircraft "violating" one's space, and it is a proximity alert, with vertical rate information applied in the case of an RA, to prevent a collision. It's not an unfair inference.

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