Midair collision between Helicopter and CRJ (AA5342) at Washington (DCA)

[marki]

For helicopter pilots:

What is the error range of altimeters?.
X00feet indicated = X 00 feet +/- actual?

How easy is it to maintain altitude at X?. Is there an allowed variability?

Altimeters for helicopters typically have an error range of **±50 to ±100 feet** under normal conditions, meaning an indicated altitude of X00 feet could be X00 ±50-100 feet. Maintaining altitude is challenging due to helicopter instability, but pilots generally aim to stay within **±100 feet** of their target altitude, with tighter tolerances in instrument flight. Environmental factors and pilot skills significantly influence precision. NVGs can give altered height perception as well.

 

[bad]

Helicopter or fixed wing it’s fair to say they are the same ie highly accurate, but they require accurate local air pressure data which is why QNH is always mentioned. If the pilot does not have the right QNH dialled in, you get errors ….

I agree with Markis10 above; altimeters in helicopters and fixed-wing aircraft are highly accurate but depend on correct QNH (local air pressure) settings. If the pilot dials in the wrong QNH, the altitude reading will be inaccurate, emphasizing the need for precise QNH updates from ATC to ensure safe operations. How many times has this gone in the other direction, however? Some maps are outdated, and the topography will also be. To make the alarm go away (PULL up), the pilot zeros the QNH. Therefore, annoying alarm distractions will be silenced until CFIT is too late.

 

[Quickstatus]

NTSB reporting CRJ altitude (from FDR plus or combined withADS-B) to be 325Ft +/- 25ft close to point of collision.

So I come back to the question: how easy is it for a helicopter like this one to maintain 200ft altitude while flying - assuming manually operated flight and at night using NVG?

 

[RSD]

I agree with Markis10 above; altimeters in helicopters and fixed-wing aircraft are highly accurate but depend on correct QNH (local air pressure) settings. If the pilot dials in the wrong QNH, the altitude reading will be inaccurate, emphasizing the need for precise QNH updates from ATC to ensure safe operations. How many times has this gone in the other direction, however? Some maps are outdated, and the topography will also be. To make the alarm go away (PULL up), the pilot zeros the QNH. Therefore, annoying alarm distractions will be silenced until CFIT is too late.

Any need to shout it in bold?

 

[marki]

Any need to shout it in bold?

By the looks of it, the intention was supposed to be the other way around, a simple mistake, I guess, easy enough to do.

i.e., "I agree with Markis10 above; "people can be way too sensitive to such minor transgression nowadays. Sign of the times? Cough cough; I am no slouch when it comes to transgressions either. I agree with Markis10 as well because the slip of the fingers can be so devastating in these circumstances.

 

[jb747]

I agree with Markis10 above; altimeters in helicopters and fixed-wing aircraft are highly accurate but depend on correct QNH (local air pressure) settings. If the pilot dials in the wrong QNH, the altitude reading will be inaccurate, emphasizing the need for precise QNH updates from ATC to ensure safe operations. How many times has this gone in the other direction, however? Some maps are outdated, and the topography will also be. To make the alarm go away (PULL up), the pilot zeros the QNH. Therefore, annoying alarm distractions will be silenced until CFIT is too late.

When you’re low flying, you rely on the radar altimeter. Any form of pull up warning is also radar based. I have no idea what you’re talking about with regard to zeroing a QNH to make a warning go away.

 

[jb747]

NTSB reporting CRJ altitude (from FDR plus or combined withADS-B) to be 325Ft +/- 25ft close to point of collision.

So I come back to the question: how easy is it for a helicopter like this one to maintain 200ft altitude while flying - assuming manually operated flight and at night using NVG?

It should be relatively easy. Helicopters are basically slow, and 200’ is high. These are army pilots…10 feet is the sort of flying they would do in some circumstances, albeit not at night. Even if they were above the height they should have been at, the separation is woefully inadequate. I think it will take them a while to get there, but this all comes back to ATC in the USA being terribly broken. It has been for many years, and I doubt that it’s going to change.

 

[straitman]

Altimeters for helicopters typically have an error range of **±50 to ±100 feet** under normal conditions, meaning an indicated altitude of X00 feet could be X00 ±50-100 feet. Maintaining altitude is challenging due to helicopter instability, but pilots generally aim to stay within **±100 feet** of their target altitude, with tighter tolerances in instrument flight. Environmental factors and pilot skills significantly influence precision. NVGs can give altered height perception as well.

I am interested to know where/how you surmise this or where you got the information from?

I cannot think of any circumstance where a helicopter could not hold accurate altitude to any degree less than a fixed wing aircraft.

 

[justinbrett]

It should be relatively easy. Helicopters are basically slow, and 200’ is high. These are army pilots…10 feet is the sort of flying they would do in some circumstances, albeit not at night. Even if they were above the height they should have been at, the separation is woefully inadequate. I think it will take them a while to get there, but this all comes back to ATC in the USA being terribly broken. I has been for many years, and I doubt that it’s going to change.

I can pretty much guarantee this is not supposed to be procedurally separated (ie the ability to set and forget) - it relies on visual separation from either the pilot or ATC. If that can't be done then the helicopter holds at a point clear of final until the path is clear - and that's probably why they have a dedicated helicopter controller.

There's also nothing stopping the CRJ descending to 200FT if it wants to. I looked up the Jeppesen charts for DCA and the helicopter route isn't even mentioned. I would have thought it deserved a mention here:

 

[Quickstatus]

the separation is woefully inadequate

Generally a 'system" design should account for potential and forseeable errors/threats whether machine or human.
In this case there appears to be no vertical separation built into the system
While there would be lessons out of this for every stakeholder, I suspect the major corrections will need to start at the Congress / FAA rather than just ATC

I looked up the Jeppesen charts for DCA and the helicopter route isn't even mentioned

Where i I find the Class Bravo maps for DCA?

I cannot think of any circumstance where a helicopter could not hold accurate altitude to any degree less than a fixed wing aircraft.

Would you say easier than Fixed wing?

 

[Quickstatus]

I cannot think of any circumstance where a helicopter could not hold accurate altitude to any degree less than a fixed wing aircraft.

Would you say easier than Fixed wing?

 

[justinbrett]

Where i I find the Class Bravo maps charts for DCA?

SkyVector: Flight Planning / Aeronautical Charts has all the charts.

There's a lot of different ones for different uses, I'm guessing the most useful is the helicopter one:

 

[straitman]

Would you say easier than Fixed wing?

Not harder or easier for either.

 

[Quickstatus]

Would the ATC have got a warning about the conflict on their screens?

 

[RSD]

Would the ATC have got a warning about the conflict on their screens?

They did - that was when they queried the Blackhawk again about whether it had the CRJ in sight and told the Blackhawk to pass behind the CRJ

 

[elanshin]

Would the ATC have got a warning about the conflict on their screens?

I think you could even faintly hear the alert in the backgrounds of some of the transmissions.

 

[jb747]

Would the ATC have got a warning about the conflict on their screens?

Apparently conflict warnings were so common, that they became normal.

 

[RSD]

Apparently conflict warnings were so common, that they became normal.

Carry on regardless? The more we find out about the arrangement there the worse it gets...

 

[marki]

When you’re low-flying, you rely on the radar altimeter. Any form of pull-up warning is also radar-based. I have no idea what you’re talking about about zeroing a QNH to make a warning go away.

Ah yes it common in the military especially Europe. I can explain a little - there are well know examples on You Tube. =>Under air crash investigation there are good examples of zeroing of QNH. So on reset of the QNH - causes the altitude to rise. To its default QNH. More to do with out dated maps near military airports, because Jeppson(civilian) charts wont have that kind of specific data. For obvious reasons - certainly map data in Russia is usually hard to come by ( truely accurate data) And looking at radar24 Russian/Ukraine airspace is avoided!

 

[moa999]

The initial suggestion was that the helo was reporting 200ft to the ATC displays (preliminary, to be confirmed)

Close but combined with the ATC instruction to cross behind the aircraft, possibly looked OK.

Hence the discussion in the last few pages on QNH settings or anything else that could alter reported altitude.

Swiss cheese and all that.