Previous in Forum: VFD on Heat Pump Compressor   Next in Forum: How birds fly over the Himalayas
Close
Close
Close
32 comments
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807

Aircraft Collision

02/02/2025 3:21 PM

The difference between Pressure Altitude,True altitude and Absolute Altitude, let's make sure we're on the same page...

..."Constantly changing, absolute altitude is the distance measurement of your airplane above the ground. Expressed in "feet AGL" (above ground level), you can also find many obstacles and airspace classifications that exist in feet above the ground.

A radar altimeter (or radio altimeter) measures altitude above the terrain presently beneath an aircraft by timing how long it takes a beam of radio waves to reflect from the ground and return to the plane. Radar altimeters generally give readings up to 2,500 feet AGL."...

..."True altitude is the vertical distance of your airplane above sea level. Commonly expressed as "feet MSL" (feet above mean sea level), many of the airspace altitudes, terrain figures, airways, and obstacles you'll find on aeronautical charts are expressed in true altitude (MSL), feet above sea level."...

..."When you set your altimeter to 29.92, you're flying at standard pressure altitude. This is the altitude of the aircraft above the standard datum plane, the theoretical location where at 15 degrees Celsius the altimeter setting will equal 29.92 inches of mercury. Many of the calculations you'll find in your POH require knowledge of what pressure altitude you'll be flying at.

All aircraft flying above 18,000 feet MSL are required to set their altimeters to 29.92 inches Hg (in the US). This means that all aircraft flying in the flight levels will have the same altimeter setting."...

Helicopters often perform "hovering" and "low-level" flying, meaning they stay at altitudes below 500 feet above ground level (AGL), especially when engaged in operations like emergency medical services, police work, and search and rescue missions, where precise maneuvering close to the ground is necessary.

https://www.boldmethod.com/blog/lists/2025/01/the-five-types-of-flying-altitudes-explained/

https://wtop.com/local/2025/02/recovery-crews-return-to-the-potomac-debris-after-the-deadly/

Are you trying to tell me that aircraft landing and taking off regularly fly within 100' of helicopter traffic?......that's insane

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#1

Re: Aircraft Collision

02/02/2025 3:44 PM

According to international aviation standards, the minimum distance an airplane is allowed to pass another plane is typically 1,000 feet of vertical separation when flying below 29,000 feet, and 2,000 feet of vertical separation above that altitude, as set by the International Civil Aviation Organization (ICAO); this is considered the standard "protected zone" around each aircraft.

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#2
In reply to #1

Re: Aircraft Collision

02/02/2025 4:21 PM

imo, that helicopter had no business being anywhere near that airplanes glidepath...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#3
In reply to #1

Re: Aircraft Collision

02/02/2025 9:54 PM

..."separation of no less than 3 nautical miles laterally and/or 1,000 feet vertically must be maintained."...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
5
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#4

Re: Aircraft Collision

02/02/2025 11:22 PM

You can quote the established rules and your personal feelings (which is fine) but you will also find that there are thousands, if not more, of approved exceptions to take into account local needs. Especially in terms of military missions.

I do agree, though, as a private pilot and a helicopter flight engineer with a couple thousand flight hours, that that particular corridor should never be used for night training missions by even the most experienced military helicopter flight crews. There are plenty of other places that kind of training could be accomplished. And local familiarity could be obtained by day flights. IMO, of course. I'm not sure military commanders would agree.

I've flown in and out of Reagan dozens of times on commercial flights and I've been a crew member on helicopters flying in and around dense urban areas. IMO, there are hundreds of lights that could've been mistaken for a fixed wing aircraft on approach, the angle of incidence between the two aircraft could have blocked the helo pilots' view behind aircraft structure, and the helo should have had two crew chiefs in the back as extra eyes keeping a lookout. One man cannot cover both sides, particularly when both pilots are trying to perform training while managing heading and altitude in a stressful position.

As with most aviation accidents this was a chain of events that ended in the worst possible way. Breaking the link by removing one link in the chain would likely have avoided any problems and everybody would've probably continued on fat, dumb and happy.

BTW, airport controllers typically call out local barometric pressure as part of other instructions or information they broadcast. A smart pilot that's just transiting the area should request that information so every aircraft altimeter in the area would reflect correct relative altitude.

Sorry, I didn't mean to get this verbose.

Register to Reply Good Answer (Score 5)
Active Contributor

Join Date: May 2017
Posts: 24
Good Answers: 3
#5
In reply to #4

Re: Aircraft Collision

02/02/2025 11:34 PM

Speaking of altimeter settings, here's another angle.

Pilots use barometric altimeters and, below 18,000 feet, must adjust them frequently as they fly into regions of higher or lower pressure.

A pressure change of 1 inch of mercury corresponds roughly to an altitude change of 1000 feet.

The evening of the crash, the local pressure rose 0.17 inches from 5PM to 9PM, corresponding to 170 feet.

If the helicopter pilots failed to reset their altimeter to the rising pressure, their altimeter could have displayed "200 feet" when they were really at 370 feet.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#7
In reply to #5

Re: Aircraft Collision

02/03/2025 12:03 AM

The helicopter was probably using AGL readings and the airplane was in its glidepath, so altimeter reading probably not that critical...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#9
In reply to #7

Re: Aircraft Collision

02/03/2025 9:55 AM

In this instance the H-60 should've been following his barometric altimeter to receive the same relative readings as other aircraft in the vicinity. There would be no reason for them to be using an AGL based radar altimeter in a terminal control area.

Also, while the airliner may have begun their approach on the runway 01 ILS system, on short final they were requested to sidestep to runway 33 and agreed. From that point on they were on visual flight rules, not instruments.

The reason for the sidestep is that it is quite normal for landing traffic to be closer than normal separation between flights at Reagan. Asking for some aircraft on final to sidestep relieves some of the congestion for arriving aircraft I don't like this system but the airport has been pressured to accommodate more and more flights over the years and sidestepping is one "solution". Thank your congressman for that. They're too lazy to go out to Dulles.

Add to that the fact that there was only one controller on duty for that approach when there are normally two. The second controller had been allowed to leave duty early. Another bad decision in a chain of bad decisions.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#13
In reply to #9

Re: Aircraft Collision

02/03/2025 12:56 PM

So they routinely break the rules at Reagan...that doesn't sound good...pressured? how can they be pressured into breaking the rules and still call themselves competent...sounds like new management is in order...

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#14
In reply to #13

Re: Aircraft Collision

02/03/2025 1:48 PM

Moderator action - Politics

The content in this post was redacted due to political discourse.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#15
In reply to #14

Re: Aircraft Collision

02/03/2025 2:54 PM

Moderator action - Politics

The content in this post was redacted due to political discourse.

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#16
In reply to #15

Re: Aircraft Collision

02/03/2025 3:14 PM

For almost three years straight in the '80's I flew into Washington National (now Reagan) every Friday night on the way home from business trips. Those Congress critters clogged up everything. Especially the bars!!! Remember, with the senate there are over 500 of them.

Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#18
In reply to #16

Re: Aircraft Collision

02/03/2025 4:48 PM

And if you’re flying first class, you could be bumped… by a narcissistic career politician,

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#19
In reply to #18

Re: Aircraft Collision

02/03/2025 5:00 PM

Well, I mostly flew out on Sunday nights to be at my customers' sites first thing Monday morning. No egoistic congress critter would ever fly on their own time. They'd fly on our time on Monday mornings, and not early.

And Sunday nights out of Reagan were usually so light I often got bumped up to 1st class as a super frequent flyer.

It was pretty much an enjoyable era to fly. Never saw sweats and flip flops back then.

Register to Reply
Guru
Hobbies - DIY Welding - Wannabeabettawelda

Join Date: May 2007
Location: Annapolis, Maryland
Posts: 7860
Good Answers: 452
#20
In reply to #19

Re: Aircraft Collision

02/03/2025 11:14 PM

The airport of last resort. Being near Annapolis, BWI is my first choice. Dulles is further away than Reagan, but the hassles with traffic and parking at Reagan make Dulles preferable over Reagan.

Or if the drive time was six hours or less, and I had the time, driving is so much less stressful.

Register to Reply Off Topic (Score 5)
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#17
In reply to #15

Re: Aircraft Collision

02/03/2025 4:41 PM

Moderator action - Politics

The content in this post was redacted due to political discourse.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#11
In reply to #5

Re: Aircraft Collision

02/03/2025 11:12 AM

And you can add to those pressure altitude variations the fact that a distraction in the cockpit to the pilot at the controls flying manually can easily add or subtract 50 or more feet to altitude in a second or two.

I remember as a student one of the hardest things to learn is to hold an altitude at +/- 100' without automatic altitude control. It's quite daunting until you gain experience. And some never do catch on.

Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#6
In reply to #4

Re: Aircraft Collision

02/02/2025 11:36 PM

Well I have no idea why the helicopter was at 300' instead of 200' if in fact that turns out to be the case, but there is no way these aircraft should be passing within 100' in any case anyway....

__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#8
In reply to #4

Re: Aircraft Collision

02/03/2025 9:50 AM

I understand that Reagan Airport had (2) two recent close calls. That's what we know of, may find more if dug deeper.

Now close calls can happen for a variety of reason. It's comes down to learning from it and mitigating it. With the understanding, that close calls can be created by a number of actions, where (2) close calls are not created by the same previous situations.

Going off topic here, it not only the tower's flight controller, its the math of how radar actually works each individual aircraft is unbelievably complex using complex and imaginary numbers.

I've pick this up when I went to college in my calculus classes, back when writing was done with a chisel and clay tablets... so I copied and pasted

this link is a more in depth read for a blog, and it did shake some cobwebs loose for me, that made it interesting...

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply
Guru
Engineering Fields - Nuclear Engineering - New Member

Join Date: Sep 2009
Location: Louisville, OH
Posts: 1828
Good Answers: 35
#12
In reply to #4

Re: Aircraft Collision

02/03/2025 12:27 PM

Hooker: Verbose is OK; that was good info from experience as a pilot.

__________________
Lehman57
Register to Reply
2
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9725
Good Answers: 1118
#10

Re: Aircraft Collision

02/03/2025 10:02 AM

Are you trying to tell me that aircraft landing and taking off regularly fly within 100' of helicopter traffic?......that's insane

Yes it is, like playing Russian Roulette, the chamber's usually empty, except once when it's not.

Register to Reply Good Answer (Score 2)
Guru
Philippines - Member - New Member Engineering Fields - Instrumentation Engineering - New Member Engineering Fields - Control Engineering - Who am I?

Join Date: Oct 2006
Location: Northern Mindanao, Philippines
Posts: 2127
Good Answers: 51
#21

Re: Aircraft Collision

02/06/2025 8:07 AM

What I don't understand is why the ATC didn't tell the chopper pilot that he had traffic to his front left. He just kept asking, "Do you have him in sight?" And chopper kept answering, "Yes, I do," while looking towards the back. A simple, "Traffic is to your ten o'clock," would have jolted the chopper pilot into looking in the right direction.

regards,

Vulcan

__________________
Miscommunication: when what people heard you say differs from what you said. Make yourself understood.
Register to Reply Score 1 for Good Answer
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#22
In reply to #21

Re: Aircraft Collision

02/06/2025 4:31 PM

I believe ATC did ask if he sees the aircraft to the left, the chopper pilot did and confirmed it, unfortunately the chopper pilot saw the wrong aircraft that was taking off and not the one on the flight path that he hit.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply Score 1 for Good Answer
Active Contributor

Join Date: May 2017
Posts: 24
Good Answers: 3
#23
In reply to #22

Re: Aircraft Collision

02/06/2025 4:51 PM

ATC only called out the specific location of the jet one time, thereafter asking only if the helicopter saw the jet. "Blancolirio" always has the best analysis, complete with ATC recordings and animated maps.

Register to Reply
Associate

Join Date: Jun 2011
Posts: 39
Good Answers: 1
#24

Re: Aircraft Collision

02/07/2025 6:06 AM

This may be of interest. The info is from own research in other fields but may be relevant.

Hooker at#4 last para set the basic. Bo1000 at #5 sort of confirms.

My research indicates planetary alignments/conjunctions effect the gravity vector, and have noted several cases as examples (but not hard proof). Others have noted similar during solar eclipses, and have called the phenomenon a 'gravity anomaly valley'. It is a near abrupt/fast minor and temporary reduction in gravity due to planetary pull countering that of the earth. Anything that has some mass has its weight reduced - on earth crust and atmosphere.

I have been looking for examples; here are some noted:

Storm Ian 28sept2022 as site passed under Jupiter; reduction in barometric press noted by Met O -wiki data, noted at the time.

1980 St Helens, gravity reduction reduced burden weight > eruption; Turkey earthquake (anticipated some event and day but not site); recent Etna violent eruption. Others in distant past (main research; were cataclysmic).

There is presently an interesting planetary situation. The argument is this: if altimeter is set during 'gravity anomaly valley', after it passes reading will be in error - biased. (a reduction in gravity is a reduction in air pressure at effected site)

Check: there should be record of such barometer transient dip, see #5; it should also be detected moving across with earth rotation.

Sorry if this is useless; its been on my mind some days now.

Register to Reply
Guru
Engineering Fields - Nuclear Engineering - New Member

Join Date: Sep 2009
Location: Louisville, OH
Posts: 1828
Good Answers: 35
#26
In reply to #24

Re: Aircraft Collision

02/07/2025 12:47 PM

Where are you from--your use of English is "interesting." The gravity effect from alignment/conjunction of planetary bodies, cannot be "abrupt/fast." The actual alignment/conjunction is, of course, very short, thus sudden, but the approach of the planets to alignment/conjunction is not sudden, but gradual. I'm also thinking that the gravity effect is minor, as you say, but so minor that it is negligible. In other words, superfluous information.

__________________
Lehman57
Register to Reply
Associate

Join Date: Jun 2011
Posts: 39
Good Answers: 1
#27
In reply to #26

Re: Aircraft Collision

02/07/2025 1:43 PM

Location the Med. English is 'economical engineering', but generally understood.

No knowledge of flight details, other than looked at FAA.pdf on 'altimeter'.

Passage of site under influence of gravity effects is quite fast and short; it is the speed of earth rotation. Moon always critical; new or full, and depending on orientation of others (Jupiter and Venus). Only effective for a few days, at right moment.

If interested look up Allais effect.

Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#25

Re: Aircraft Collision

02/07/2025 11:27 AM

Preliminary investigation indicates that the helo pilots were probably flying with NVG's (night vision googles). That would explain a lot. NVG's have a very restrictive field of view.

Back in my day only the pilot actually flying the aircraft was allowed to be under NVG concentrating on mission objectives. Everybody else was supposed to have eyes out the windshield looking for obstacles that the flying pilot could easily miss. More than one helo was lost to trees or power wires or a wingman before that lesson was learned.

Now I'm sure that NVG's have improved somewhat since my day but, in this case, if both pilots were using NVG's and the one non-flying crew member in the back had a restricted view this was a recipe for disaster in congested airspace.

It's also very easy to lose touch with important info only seen on the instrument panel, such as altitude. Especially since it's very difficult to visually judge altitude over water at night.

I have personal experience with that as a flight engineer in a Chinook watching a sling load through the hell hole in the bottom of the Chinook. It was my responsibility to tell the pilots how high the load was off the ground during the approach to the drop zone. However, at night, due to my limited field of view through the hole we often had the crew chief on the right door make the initial height call-outs from about 100' down to where the flight engineer over the hole could regain the height perspective. The man in the door had a better reference to trees, building, etc, to judge height in the dark.

Altitude close to the ground in a helo can be a very tricky and dangerous business.

Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#28

Re: Aircraft Collision

02/08/2025 9:17 AM

More detailed reports are coming out.

It’s been revealed that the NTSB that the helicopter was operating 30+ meters above the maximum height allowed. Along with the ADS-B turned off.

“The Automatic Dependent Surveillance–Broadcast (ADS-B) is a technology that allows aircraft to broadcast their position and other data to air traffic control (ATC). ADS-B is used to improve the accuracy and reliability of aircraft tracking, which can enhance safety and efficiency in aviation.”

I’m sure more will come out and the reason why,… speculating, it’ll be pilot era.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply
Guru
Engineering Fields - Aerospace Engineering - Member United States - Member - Army Vet in the aviation industry

Join Date: Mar 2008
Location: Bridgewater, Va.
Posts: 2169
Good Answers: 119
#29
In reply to #28

Re: Aircraft Collision

02/08/2025 11:26 AM

I saw the ADS-B being off report. It had to be on their start-up checklist to turn it on.Heads should roll for this, right up to the company commander.

Register to Reply
Guru

Join Date: Oct 2008
Posts: 42377
Good Answers: 1690
#30

Re: Aircraft Collision

02/12/2025 5:07 PM

Congress is guilty of overcrowding this airport because it is CONVENIENT for them.

They kept approving more flights..................................................for years.

"Kaine also warned of the potential for collisions if more flights were approved for the busy airport while speaking to reporters last year.

Add to that control tower under-staffing (for years) was a significant factor.

Register to Reply
Guru
Hobbies - CNC - New Member Hobbies - DIY Welding - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2007
Posts: 23518
Good Answers: 419
#31
In reply to #30

Re: Aircraft Collision

02/12/2025 6:35 PM

if air traffic controllers were fully staffed would more then likely solve that.

Maybe DOGE may put those flights for politicians on the chopping block would be fine with me.

__________________
“ When people get what they want, they are often surprised when they get what they deserve " - James Wood
Register to Reply
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 33233
Good Answers: 1807
#32

Re: Aircraft Collision

02/14/2025 9:32 PM
__________________
All living things seek to control their own destiny....this is the purpose of life
Register to Reply
Register to Reply 32 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Bo1000 (2); Brave Sir Robin (1); Hooker (8); Lehman57 (2); lyn (1); oldwidget (2); phoenix911 (6); Rixter (1); SolarEagle (8); Vulcan (1)

Previous in Forum: VFD on Heat Pump Compressor   Next in Forum: How birds fly over the Himalayas

Advertisement