Altimeter (All) Page: 4 of 4

Musician
January 29, 2026, 13:55:00 GMT
permalink Post: 12029155

Quote:

Originally Posted by Ver5pen

weird that they don’t even mention the Blackhawk PF’s straying from altitude constraints, the IP repeatedly tells her about her deviations multiple times as per the transcript, baro altitude limitations or not they were both aware she wasn’t meeting the limits of the corridor (that the margins are so fine in that airspace is absurd of course)

It's in the findings.
https://www.ntsb.gov/investigations/...CA25MA108.aspx

31. Due to additive allowable tolerances of the helicopter’s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter’s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4.

Quote:

Originally Posted by Ver5pen

that recreation is incredible, kudos to NTSB I don’t know why they chose to create it from the IP’s (RHS)’s point of view though, the PF was LHS and arguably had a better view of the CRJ the entire time

I'm guessing because the IP reported the aircraft in sight, the PF didn't.

27. The PAT25 instructor pilot did not positively identify flight 5342 at the time of the initial traffic advisory despite his statement that he had the traffic in sight and his request for visual separation.

Subjects Altimeter (All) Barometric Altimeter Blackhawk (H-60) CRJ Findings NTSB PAT25 Route 4 Separation (ALL) Traffic in Sight Visual Separation

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JohnDixson
January 31, 2026, 18:23:00 GMT
permalink Post: 12030315

This was supposed to be a checkride including Night vision Goggle usage and a bunch of submittals regarding the use and accuracy of the bardo metric altimeter system, and not much, if anything regarding the radar altimeter system accuracy.
The UH-60 Maintenance Test Flight Manual includes a barometric altimeter accuracy check, which is accomplished by calling the tower for the local altimeter setting, set the altimeter accordingly and comparing the altimeter readout to the elevation of that heliport/airport. THE ACCEPTED MAXIMUM ERROR IS 70 FEET. So, the baro altimeter readout can be 70 ft off and you are OK to fly: VFR or IFR.

The radar altimeter ( APN-171 or later APN-209 ) accuracy is similar at +/- 3 ft then 3% of indicated altitude, so, for the H-4 Route Maximum altitude of 200 ft. The Rad Alt could be as much as 9 ft off.

The NVGs do show Rad Alt.

Haven\x92t seen any submittal indicating the Rad Alt was inoperative or unusable.

Subjects Altimeter (All) Barometric Altimeter IFR Night Vision Goggles (NVG) Radar Radio Altimeter VFR

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DaveReidUK
January 31, 2026, 21:00:00 GMT
permalink Post: 12030376

Quote:

Originally Posted by JohnDixson

None of the references to NVGs in the hearing made mention of a HUD capability.

The Helicopter Operations presentation included a slide stating that pilots are "Trained to use barometric altimeter to navigate helicopter route ceilings".

Subjects Altimeter (All) Barometric Altimeter HUD IFR Night Vision Goggles (NVG) Radar Radio Altimeter VFR

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BFSGrad
January 31, 2026, 22:24:00 GMT
permalink Post: 12030414

Quote:

Originally Posted by JohnDixson

The radar altimeter ( APN-171 or later APN-209 ) accuracy is similar at +/- 3 ft then 3% of indicated altitude, so, for the H-4 Route Maximum altitude of 200 ft. The Rad Alt could be as much as 9 ft off. The NVGs do show Rad Alt. Haven\x92t seen any submittal indicating the Rad Alt was inoperative or unusable.

Extensive discussion in the interview transcripts about why all of the DC area helicopter pilots (medical, LEO, military) use baro rather than radar altitude when flying the DC helicopter routes.

Subjects Altimeter (All) Night Vision Goggles (NVG) Radar Radio Altimeter

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Musician
February 18, 2026, 01:30:00 GMT
permalink Post: 12038924

Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion.
.

Altimeter testing showed that the 100-ft pressure altitude discrepancy seen in the FDR data for the accident flight was observed on three other UH-60L helicopters operated by the 12th Aviation Battalion. These altimeter testing results also showed that the pressure altitude data recorded by the helicopters\x92 FDRs, when corrected for local conditions, was representative of what was indicated on the right side altimeter. Therefore, the FDR pressure altitude data for the accident helicopter, when corrected for local conditions, was likely representative of what was indicated on the IP\x92s barometric altimeter during the accident flight.

[...]. The NTSB concludes that, due to additive allowable tolerances of the helicopter\x92s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter\x92s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4.

For the northern segment of Route 4, which included the area of the collision, of the 523 flights analyzed, 260 flights (49%) were identified as exceeding route altitude limitations at some point during the flight. Had the error tolerances of barometric altimeters been considered during design of the helicopter route maximum altitudes, the incompatibility of a 200-ft ceiling and barometric altimeter errors may have been identified.

Subjects Altimeter (All) Barometric Altimeter Final Report NTSB PAT25 Route 4 Route Altitude

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MechEngr
February 18, 2026, 02:03:00 GMT
permalink Post: 12038935

Quote:

Originally Posted by Musician

Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion.

They requested visual separation and gave affirmation they had the other aircraft in sight. Failing to check the altimeter to a known datum was the least contributor.

Subjects Altimeter (All) Final Report Separation (ALL) Visual Separation

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Musician
February 18, 2026, 02:50:00 GMT
permalink Post: 12038946

Quote:

Originally Posted by MechEngr

They requested visual separation and gave affirmation they had the other aircraft in sight. Failing to check the altimeter to a known datum was the least contributor.

Yes, but the visual separation was the responsibility of the PIC instructor, not the PF.

You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist?

Subjects Altimeter (All) Separation (ALL) Visual Separation

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Someone Somewhere
February 18, 2026, 05:53:00 GMT
permalink Post: 12038980

Quote:

Originally Posted by Musician

I thought an instrument check was normally part of a pre-flight?

I am not sure checking that the altimeter matches field elevation while stationary on the pad would help, as it sounds like the issue is the altimeter reading changing when the rotor is loaded.

In either case, calling ~100ft 'vertical separation' is basically false.

Subjects Altimeter (All) Separation (ALL) Vertical Separation Visual Separation

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ATC Watcher
February 18, 2026, 16:22:00 GMT
permalink Post: 12039242

The 100ft in the altimeter is within IFR tolerance , not really the point here , yes you should check against elevation airfield before start , but we learn there is a small discrepancy when on the ground and when the rotor blows over the static holes, and ATC will check again in flight the alt against mode C, it is mandatory on first contact with ATC , but mode C is calibrated on 1013 not QNH , anyway not the major cause here, just another hole on the cheese that night .

As to the lack of experience of the PF , I think 56 h of flying visual and manual an helicopter is significantly more important experience wise that the same number on say, a 747 .I also do not think this was factor.
The reasons and direct causes of this accident are within the 50 NTSB recommendations , not in the altimeter or experience of the PF , unless she had a couple of close calls herself doing visual separation at night before and did not learn from that.

Last edited by ATC Watcher; 18th February 2026 at 16:35 .

Subjects ATC Altimeter (All) Close Calls IFR NTSB QNH Separation (ALL) Visual Separation

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Lonewolf_50
February 18, 2026, 17:39:00 GMT
permalink Post: 12039290

For Chiefttp:
The question of currency, proficiency, and recency fairly leap off of the page, yes.

Quote:

Originally Posted by DaveReidUK

At the height the collision occurred, there would never have been a TCAS RA.

Inconvenient facts never stopped a lawyer from bringing a case to court, though.

Quote:

Originally Posted by Musician

Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion.

No, it does not.

Quote:

Originally Posted by Musician

Yes, but the visual separation was the responsibility of the PIC instructor, not the PF.

Wrong. Visual lookout is a responsibility for all members of the crew. That's a shared responsibility, and briefed before every flight. Note that in a Blackhawk, there are a variety of zones where the pilots are effectively blind (starting at about the four o'clock position and reaching to about 8 o'clock position) but the forward quarter isn't usually one of those. (Won't comment on the goggle issue here...)

Quote:

Originally Posted by Musician

You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist?

Not just pre-flight checks.
I am not sure how much low level, over water, at night flying that you have done, but I have done quite a bit of that. If you are flying in such a regime, and there is a substantial mismatch between your radalt, and your baralt, and you have a hard altitude limit, you don't ignore your radalt.

Subjects Altimeter (All) Blackhawk (H-60) Final Report Radio Altimeter Separation (ALL) TCAS (All) TCAS RA Visual Separation

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island_airphoto
February 19, 2026, 04:18:00 GMT
permalink Post: 12039465

Quote:

Originally Posted by Musician

I check my altimeter every time I fly, I think pretty much everyone does. An instructor is of course responsible for what his student does, so there is that.

Subjects Altimeter (All) Separation (ALL) Visual Separation

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Ver5pen
February 19, 2026, 14:18:00 GMT
permalink Post: 12039724

Quote:

Originally Posted by Musician

Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion.
.

repeatedly in the CVR transcript of the Blackhawk the instructor tells the PF they are straying from their clearance

the PF had also shown their handling skills were not to standard earlier in the check ride (I\x92ve seen it mentioned their abandoning a manoeuvre earlier would\x92ve been a fail normally) hence monitoring their trainees parameters would\x92ve been even more taxing for the instructor

I don\x92t know how anyone can pretend these things didn\x92t at least play a part in the Swiss cheese.

if the PF had been as equally capable as the instructor and performing their scan (the CGI reenactment shows that much of the CRJ\x92s flatboats occurred within the PF\x92s side of the scan) would the outcome have been different? Possibly.

the conduct of that flight was the final hole in the Swiss cheese arguably

Subjects Altimeter (All) Barometric Altimeter Blackhawk (H-60) CVR Final Report NTSB PAT25 Route 4 Route Altitude

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punkalouver
February 19, 2026, 17:02:00 GMT
permalink Post: 12039783

Quote:

Originally Posted by Musician

When the altimeter setting is placed in the aircraft on the ground, the pilot should take note of how much difference there is from actual field elevation and then consider what should be done for compensation for any error. On most VFR flights, a 100' error does not have much relevance. On the other hand, if you were to know that you are going to pass extremely close to something that you do not want to be close to, then it can become significant. An example might be for the people who like to fly 100 feet vertically from airspace that they are not allowed to enter. This situation might be another example where good airmanship can make a difference(specifically to compensating for an altimeter error).

I have not read this report, as I am deep into many other ones these days but I did take a quick glance on page 242 that was referenced and it talks about altimeter additive errors. The report states: "The allowable tolerances are additive, with the total error having the potential of exceeding 100 ft.". The report also states: "The NTSB concludes that, due to additive allowable tolerances of the helicopter\x92s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter\x92s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4".

My question to other people on this thread is: Did the NTSB do some sort of evaluation of this particular helicopter in order to come to a reasonable conclusion that all errors were in such a way that they were all in the direction of resulting in the helicopter being higher than indicated as opposed to errors potentially cancelling each other out(or partially so)?

Subjects Altimeter (All) Barometric Altimeter NTSB PAT25 Route 4 Separation (ALL) VFR Visual Separation

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Musician January 29, 2026, 13:55:00 GMT permalink Post: 12029155	Quote: Originally Posted by Ver5pen weird that they don’t even mention the Blackhawk PF’s straying from altitude constraints, the IP repeatedly tells her about her deviations multiple times as per the transcript, baro altitude limitations or not they were both aware she wasn’t meeting the limits of the corridor (that the margins are so fine in that airspace is absurd of course) It's in the findings. https://www.ntsb.gov/investigations/...CA25MA108.aspx 31. Due to additive allowable tolerances of the helicopter’s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter’s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4. . Quote: Originally Posted by Ver5pen that recreation is incredible, kudos to NTSB I don’t know why they chose to create it from the IP’s (RHS)’s point of view though, the PF was LHS and arguably had a better view of the CRJ the entire time I'm guessing because the IP reported the aircraft in sight, the PF didn't. 27. The PAT25 instructor pilot did not positively identify flight 5342 at the time of the initial traffic advisory despite his statement that he had the traffic in sight and his request for visual separation. Subjects Altimeter (All) Barometric Altimeter Blackhawk (H-60) CRJ Findings NTSB PAT25 Route 4 Separation (ALL) Traffic in Sight Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. No recorded likes for this post (could be before pprune supported 'likes'). Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
JohnDixson January 31, 2026, 18:23:00 GMT permalink Post: 12030315	This was supposed to be a checkride including Night vision Goggle usage and a bunch of submittals regarding the use and accuracy of the bardo metric altimeter system, and not much, if anything regarding the radar altimeter system accuracy. The UH-60 Maintenance Test Flight Manual includes a barometric altimeter accuracy check, which is accomplished by calling the tower for the local altimeter setting, set the altimeter accordingly and comparing the altimeter readout to the elevation of that heliport/airport. THE ACCEPTED MAXIMUM ERROR IS 70 FEET. So, the baro altimeter readout can be 70 ft off and you are OK to fly: VFR or IFR. The radar altimeter ( APN-171 or later APN-209 ) accuracy is similar at +/- 3 ft then 3% of indicated altitude, so, for the H-4 Route Maximum altitude of 200 ft. The Rad Alt could be as much as 9 ft off. The NVGs do show Rad Alt. Haven\x92t seen any submittal indicating the Rad Alt was inoperative or unusable. Subjects Altimeter (All) Barometric Altimeter IFR Night Vision Goggles (NVG) Radar Radio Altimeter VFR Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
DaveReidUK January 31, 2026, 21:00:00 GMT permalink Post: 12030376	Quote: Originally Posted by JohnDixson This was supposed to be a checkride including Night vision Goggle usage and a bunch of submittals regarding the use and accuracy of the bardo metric altimeter system, and not much, if anything regarding the radar altimeter system accuracy. The UH-60 Maintenance Test Flight Manual includes a barometric altimeter accuracy check, which is accomplished by calling the tower for the local altimeter setting, set the altimeter accordingly and comparing the altimeter readout to the elevation of that heliport/airport. THE ACCEPTED MAXIMUM ERROR IS 70 FEET. So, the baro altimeter readout can be 70 ft off and you are OK to fly: VFR or IFR. The radar altimeter ( APN-171 or later APN-209 ) accuracy is similar at +/- 3 ft then 3% of indicated altitude, so, for the H-4 Route Maximum altitude of 200 ft. The Rad Alt could be as much as 9 ft off. The NVGs do show Rad Alt. Haven\x92t seen any submittal indicating the Rad Alt was inoperative or unusable. None of the references to NVGs in the hearing made mention of a HUD capability. The Helicopter Operations presentation included a slide stating that pilots are "Trained to use barometric altimeter to navigate helicopter route ceilings". Subjects Altimeter (All) Barometric Altimeter HUD IFR Night Vision Goggles (NVG) Radar Radio Altimeter VFR Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
BFSGrad January 31, 2026, 22:24:00 GMT permalink Post: 12030414	Quote: Originally Posted by JohnDixson The radar altimeter ( APN-171 or later APN-209 ) accuracy is similar at +/- 3 ft then 3% of indicated altitude, so, for the H-4 Route Maximum altitude of 200 ft. The Rad Alt could be as much as 9 ft off. The NVGs do show Rad Alt. Haven\x92t seen any submittal indicating the Rad Alt was inoperative or unusable. Extensive discussion in the interview transcripts about why all of the DC area helicopter pilots (medical, LEO, military) use baro rather than radar altitude when flying the DC helicopter routes. Subjects Altimeter (All) Night Vision Goggles (NVG) Radar Radio Altimeter Links are to this post in the relevant subject page so that this post can be seen in context. 3 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 18, 2026, 01:30:00 GMT permalink Post: 12038924	Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion. . Altimeter testing showed that the 100-ft pressure altitude discrepancy seen in the FDR data for the accident flight was observed on three other UH-60L helicopters operated by the 12th Aviation Battalion. These altimeter testing results also showed that the pressure altitude data recorded by the helicopters\x92 FDRs, when corrected for local conditions, was representative of what was indicated on the right side altimeter. Therefore, the FDR pressure altitude data for the accident helicopter, when corrected for local conditions, was likely representative of what was indicated on the IP\x92s barometric altimeter during the accident flight. [...]. The NTSB concludes that, due to additive allowable tolerances of the helicopter\x92s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter\x92s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4. For the northern segment of Route 4, which included the area of the collision, of the 523 flights analyzed, 260 flights (49%) were identified as exceeding route altitude limitations at some point during the flight. Had the error tolerances of barometric altimeters been considered during design of the helicopter route maximum altitudes, the incompatibility of a 200-ft ceiling and barometric altimeter errors may have been identified. Subjects Altimeter (All) Barometric Altimeter Final Report NTSB PAT25 Route 4 Route Altitude Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
MechEngr February 18, 2026, 02:03:00 GMT permalink Post: 12038935	Quote: Originally Posted by Musician Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion. They requested visual separation and gave affirmation they had the other aircraft in sight. Failing to check the altimeter to a known datum was the least contributor. Subjects Altimeter (All) Final Report Separation (ALL) Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. 4 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Musician February 18, 2026, 02:50:00 GMT permalink Post: 12038946	Quote: Originally Posted by MechEngr They requested visual separation and gave affirmation they had the other aircraft in sight. Failing to check the altimeter to a known datum was the least contributor. Yes, but the visual separation was the responsibility of the PIC instructor, not the PF. You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist? Subjects Altimeter (All) Separation (ALL) Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. No recorded likes for this post (could be before pprune supported 'likes'). Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Someone Somewhere February 18, 2026, 05:53:00 GMT permalink Post: 12038980	Quote: Originally Posted by Musician Yes, but the visual separation was the responsibility of the PIC instructor, not the PF. You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist? I thought an instrument check was normally part of a pre-flight? I am not sure checking that the altimeter matches field elevation while stationary on the pad would help, as it sounds like the issue is the altimeter reading changing when the rotor is loaded. In either case, calling ~100ft 'vertical separation' is basically false. Subjects Altimeter (All) Separation (ALL) Vertical Separation Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. 3 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
ATC Watcher February 18, 2026, 16:22:00 GMT permalink Post: 12039242	The 100ft in the altimeter is within IFR tolerance , not really the point here , yes you should check against elevation airfield before start , but we learn there is a small discrepancy when on the ground and when the rotor blows over the static holes, and ATC will check again in flight the alt against mode C, it is mandatory on first contact with ATC , but mode C is calibrated on 1013 not QNH , anyway not the major cause here, just another hole on the cheese that night . As to the lack of experience of the PF , I think 56 h of flying visual and manual an helicopter is significantly more important experience wise that the same number on say, a 747 .I also do not think this was factor. The reasons and direct causes of this accident are within the 50 NTSB recommendations , not in the altimeter or experience of the PF , unless she had a couple of close calls herself doing visual separation at night before and did not learn from that. Last edited by ATC Watcher; 18th February 2026 at 16:35 . Subjects ATC Altimeter (All) Close Calls IFR NTSB QNH Separation (ALL) Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. 2 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Lonewolf_50 February 18, 2026, 17:39:00 GMT permalink Post: 12039290	For Chiefttp: The question of currency, proficiency, and recency fairly leap off of the page, yes. Quote: Originally Posted by DaveReidUK At the height the collision occurred, there would never have been a TCAS RA. Inconvenient facts never stopped a lawyer from bringing a case to court, though. Quote: Originally Posted by Musician Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion. No, it does not. Quote: Originally Posted by Musician Yes, but the visual separation was the responsibility of the PIC instructor, not the PF. Wrong. Visual lookout is a responsibility for all members of the crew. That's a shared responsibility, and briefed before every flight. Note that in a Blackhawk, there are a variety of zones where the pilots are effectively blind (starting at about the four o'clock position and reaching to about 8 o'clock position) but the forward quarter isn't usually one of those. (Won't comment on the goggle issue here...) Quote: Originally Posted by Musician You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist? Not just pre-flight checks. I am not sure how much low level, over water, at night flying that you have done, but I have done quite a bit of that. If you are flying in such a regime, and there is a substantial mismatch between your radalt, and your baralt, and you have a hard altitude limit, you don't ignore your radalt. Subjects Altimeter (All) Blackhawk (H-60) Final Report Radio Altimeter Separation (ALL) TCAS (All) TCAS RA Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. 3 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
island_airphoto February 19, 2026, 04:18:00 GMT permalink Post: 12039465	Quote: Originally Posted by Musician Yes, but the visual separation was the responsibility of the PIC instructor, not the PF. You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist? I check my altimeter every time I fly, I think pretty much everyone does. An instructor is of course responsible for what his student does, so there is that. Subjects Altimeter (All) Separation (ALL) Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
Ver5pen February 19, 2026, 14:18:00 GMT permalink Post: 12039724	Quote: Originally Posted by Musician Page 242 ff. in the final report pretty much exonorates the PF in the helicopter, in my opinion. . Altimeter testing showed that the 100-ft pressure altitude discrepancy seen in the FDR data for the accident flight was observed on three other UH-60L helicopters operated by the 12th Aviation Battalion. These altimeter testing results also showed that the pressure altitude data recorded by the helicopters\x92 FDRs, when corrected for local conditions, was representative of what was indicated on the right side altimeter. Therefore, the FDR pressure altitude data for the accident helicopter, when corrected for local conditions, was likely representative of what was indicated on the IP\x92s barometric altimeter during the accident flight. [...]. The NTSB concludes that, due to additive allowable tolerances of the helicopter\x92s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter\x92s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4. For the northern segment of Route 4, which included the area of the collision, of the 523 flights analyzed, 260 flights (49%) were identified as exceeding route altitude limitations at some point during the flight. Had the error tolerances of barometric altimeters been considered during design of the helicopter route maximum altitudes, the incompatibility of a 200-ft ceiling and barometric altimeter errors may have been identified. repeatedly in the CVR transcript of the Blackhawk the instructor tells the PF they are straying from their clearance the PF had also shown their handling skills were not to standard earlier in the check ride (I\x92ve seen it mentioned their abandoning a manoeuvre earlier would\x92ve been a fail normally) hence monitoring their trainees parameters would\x92ve been even more taxing for the instructor I don\x92t know how anyone can pretend these things didn\x92t at least play a part in the Swiss cheese. if the PF had been as equally capable as the instructor and performing their scan (the CGI reenactment shows that much of the CRJ\x92s flatboats occurred within the PF\x92s side of the scan) would the outcome have been different? Possibly. the conduct of that flight was the final hole in the Swiss cheese arguably Subjects Altimeter (All) Barometric Altimeter Blackhawk (H-60) CVR Final Report NTSB PAT25 Route 4 Route Altitude Links are to this post in the relevant subject page so that this post can be seen in context. 1 recorded likes for this post. Reply to this quoting this original post. You need to be logged in. Not available on closed threads.
punkalouver February 19, 2026, 17:02:00 GMT permalink Post: 12039783	Quote: Originally Posted by Musician Yes, but the visual separation was the responsibility of the PIC instructor, not the PF. You are of the opinion they should've checked that the altimeter was working correctly? Is that a normal item on a pre-flight checklist? When the altimeter setting is placed in the aircraft on the ground, the pilot should take note of how much difference there is from actual field elevation and then consider what should be done for compensation for any error. On most VFR flights, a 100' error does not have much relevance. On the other hand, if you were to know that you are going to pass extremely close to something that you do not want to be close to, then it can become significant. An example might be for the people who like to fly 100 feet vertically from airspace that they are not allowed to enter. This situation might be another example where good airmanship can make a difference(specifically to compensating for an altimeter error). I have not read this report, as I am deep into many other ones these days but I did take a quick glance on page 242 that was referenced and it talks about altimeter additive errors. The report states: "The allowable tolerances are additive, with the total error having the potential of exceeding 100 ft.". The report also states: "The NTSB concludes that, due to additive allowable tolerances of the helicopter\x92s pitot-static/altimeter system, it is likely that the crew of PAT25 observed a barometric altimeter altitude about 100 ft lower than the helicopter\x92s true altitude, resulting in the crew erroneously believing that they were under the published maximum altitude for Route 4". My question to other people on this thread is: Did the NTSB do some sort of evaluation of this particular helicopter in order to come to a reasonable conclusion that all errors were in such a way that they were all in the direction of resulting in the helicopter being higher than indicated as opposed to errors potentially cancelling each other out(or partially so)? Subjects Altimeter (All) Barometric Altimeter NTSB PAT25 Route 4 Separation (ALL) VFR Visual Separation Links are to this post in the relevant subject page so that this post can be seen in context. No recorded likes for this post (could be before pprune supported 'likes'). Reply to this quoting this original post. You need to be logged in. Not available on closed threads.

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