I just have to wonder (aloud) whether an error of 78 feet is really indicative of a “malfunction” or just standard instrument error for something that might (hypothetically) not be intended or expected to be accurate to within less than about a hundred feet on either side of the actual altitude.
I just pulled up the system description for the radio altimeter on a transport category aircraft. I’m going to assume the helicopter has a similar level of tech, quite possibly the same supplier and maybe even same system.
The radalt operates below 2500ft. When 0-500ft off the ground the accuracy is +/- 2 feet. When 500-2500 feet, the accuracy is +/-3ft.
This system uses four antenna going to two transceivers (so two radalt systems). In normal operation the pilot and copilot will see output from different systems. The displays will flag a signal if one has failed and the display is showing from the same one (common source). Another signal will indicate if there’s a significant mismatch/disagree.
Planes and helicopters and systems like autopilot or auto throttle need to know where the aircraft is in space, to avoid pancaking into the ground. A 78 foot error is catastrophic.
I don’t think it’s the radar altimeter that had the possible error.
Is there a steam gauge altimeter that commercial pilots use that’s different from what the transponder is using?
The incident helicopter is being reported as a UH-60L. Believe it or not, the User’s Manual is available from the Defense Technical Information Center (DTIC).
(PDF, if that bothers anyone.)
Page 2-18 (and the legend on Page 2-19) indicates the instrument panel has gauges for both the radar altimeter and the barometric one, directly adjacent to each other, so I guess it’s up to the pilot to choose which one they believe if they notice they disagree.
Early information from the chopper cockpit has been released.
There’s a press conference video embedded in this article.
Link Helicopter may have missed key instruction before collision: NTSB – NBC4 Washington
There have been numerous discussions here about this basic fault. The exact same failure to hear ATC instructions was also a contributing factor to the biggest air disaster of all time at Tenerife. But bureaucratic inertia prevails.
Which one you use depends on context. ATC procedures such as the helicopter route altitude requirements would almost exclusively be based on the barometric altimeter.
Is it necessarily “bureaucratic” inertia? I know it’s technically possible to have a radio that can both send and receive simultaneously (full-duplex), but before I label this a “bureaucratic” problem, I’d want to know if there is some practical reason that full-duplex would be disfavored for air traffic communications.
Honestly, I am thinking more and more that (1) the helicopter never should have requested to maintain visual separation, (2) ATC never should have granted it under the circumstances, and (3) in the final instant, ATC should have given positive direction to the helicopter to adjust heading and altitude rather than a vague, easily stepped on, instruction that assumed the helicopter had a visual on the correct aircraft.
Oh, but before all that, (0) it seems like a famously bad idea to have the helicopter routes crossing directly under (or intersecting, by some accounts) the approach to one of the busiest airports in the country. Absolutely terrible.
This is my non-commercial gut feeling. Crossing under the path of a runway approach as a matter of routine seems like an aviation accident in the making. As has often been discussed, accidents are often the result of more than one mistake. Here we possibly have: bad communication, missed communication, assumption of runway/aircraft related to communication, failure to check for aircraft that might be on short final, incorrectly maintained altitude, ADS-B turned off… there are certainly more.
Except that this procedure has been used successfully for decades. None of the players had any reason to suddenly decide it wasn’t a suitable procedure on this particular night. If you’re going to suggest it shouldn’t have been used that night, and I agree, you’re really saying it should never have been used and should not be a separation method at all, anywhere.
Unless things have change a lot in the last few decades, the radar altimeter measures above ground level, the barometric altimeter measures above mean sea level. Both are important and used for different things. For dealing with ATC above mean sea level is used since every aircraft in their area is above different terrain.
The procedure (visual separation) never should have been used for crossing flight paths at night for that particular helo route and that particular airport given how busy it regularly is. It should not have taken dozens of deaths to arrive at that conclusion, but here we are.
Consider also: how confident are you that visual separation has been used under like circumstances for decades? If other helo pilots and/or other ATCs had more sense, then point of fact, no, it wouldn’t have been used for decades under those circumstances. At least not routinely, because it would not have been routinely requested or granted.
People will use the regulations and procedures made available to them. I don’t fly in the US but from what I read, night visual separation is used regularly because the rules allow it to be used. In my part of the world visual separation at night is not legal and therefore no one asks for it and no one grants it.
ETA: Just like in the US you can be cleared to land when you’re several aircraft back in the sequence and the runway is not actually clear. The American system seems to favour relieving the air traffic controller of responsibility by putting that responsibility back on the PIC.
I have felt… challenged?..at times about the FAA when reading about different accidents and regulations and allowances over the years. I have not taken the time to fully research my impressions to see if they are valid, nor fully articulate the points that I struggle with.
Fully acknowledging that is is more “gut feel” than “fact”, I think there’s a conflict of interest between the FAA’s role as the Regulatory Agency, the procedures/reality that seems to make them heavily subject to the American Congress and therefore lobbying, and the fact that, I think, they operate airports and ATC and whatnot and have an interest in the business of it all.
I don’t recall from other posts where you operate from as a pilot, but the differences you mention sort of add to this impression that I have.
I think it’s different in Canada (Transport Canada, who I interact with for certification, doesn’t manage ATC for example) but I know very little about the operational and legal/authority side of things.
I agree that there’s often a sense of “that which isn’t forbidden is permitted” in this industry but proper regulatory oversight (and engineering ethics, at least) without a conflict of interest to keep operations going no matter what is to recognize that the correct safety perspective is “that which isn’t permitted needs to be verified as permissible…or forbidden”.
Yes but define “successfully”. There have been 23 near midair collisions between passenger planes and helicopters at DCA since 1988.
I agree, it should never have been a procedure.
Sounds very successful! 
The American air traffic control system works very well on the whole as far as I can tell. You guys have a heap of airplanes to move around the sky and it happens day in day out with very few hiccups. There is the odd procedure that makes outsiders raise their eyebrows a bit but it’s been working well you for a long time. There will always be room for improvement and there is a risk that as aviation becomes busier the procedures that have served the industry well for so long might become unfit for purpose.
I don’t think visual separation should ever be used at night but I understand that pilots and controllers who have used it their entire career have had constant subtle reinforcement (nothing bad happened this time) that it works and is safe… enough.
Back when I was actively flying the “steam gauge” altimeter (as opposed to some electronic or GPS gizmo) was required to be accurate within 50 feet. That was a civilian standard for general aviation. I’d expect the military standard to be at least that.
It is possible for altimeters to just plain malfunction - happened to me once when the pitot-static system had a blockage that couldn’t be detected on the ground during pre-flight by a civilian general aviation pilot. I noticed just after take-off and simply followed the airport traffic pattern around and landed again. But that was during the day without other traffic around.
It is possible the altimeter wasn’t properly set prior to flight.
Airline passengers have experienced serious disruptions at Washington’s Reagan National Airport because of new rules that trigger runway closures when President Donald Trump flies to and from the White House aboard his helicopter, according to people aware of the restrictions, flight tracking data and federal records.
The stricter requirements — imposed by the Federal Aviation Administration after the midair collision of an Army helicopter and American Airlines passenger jet last month that killed 67 people — have forced dozens of airliners bound for National to circle in holding patterns or divert to other airports including Dulles International, Baltimore-Washington International Marshall and Richmond International…
The policy change quickly had an impact. On Feb. 14, when Trump left the White House on the first leg of a trip to Florida, roughly 30 airliners bound for National were kept circling in the sky, publicly available flight tracking data shows. At least nine aircraft diverted to other airports. Similar disruptions have happened in the days since, the data shows.
New rules after tragedy shut National runways when Trump boards Marine One [Washington Post]
If one root cause of the tragedy was that Reagan is too popular and heavily used for its size and location, this seems like a good first step to dampen that popularity a bit. Hopefully.