Posts about: "PAT25" [Posts: 121 Page: 7 of 7]¶

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)?