"Interference as a singular cause appears to be extremely improbable."
Interference is mentioned a few times in the report as likely not being the cause or at least sole cause. The only entity seeming to push interference as a cause was Boeing, which led to this remark:
"We are not aware that interference has been conclusively identified as the explanation for the radio altimeter anomalies. In fact, some airlines have found that their incidence of radio altimeter anomalies decreased when they chose to install the new gaskets. If the conclusions here are intended to be DSB conclusions, rather than conclusions of Boeing and the airlines, the text should be revised to indicate they are DSB conclusions." in which they struck out the text "The negative values of the radio height were an indication of interference"
Was it due to interference? Otherwise this seems specious.
The Wikipedia entry [1] has a good overview, as does this Medium post [2]. In the flight 1951 crash there were actually 2 altimeters for redundancy, but due to human error they were configured so that 1 faulty altimeter affected the autothrottle:
> While on final approach for landing, the aircraft was about 2,000 ft (610 m) above ground, when the left-hand (captain's) radio altimeter suddenly changed from 1,950 feet (590 m) to read −8 feet (−2.4 m) height, although the right-hand (co-pilot's) radio altimeter functioned correctly. The voice recording showed that the crew was given an audible warning signal (landing gear warning horn) that indicated that the aircraft's landing gear should be down, as the aircraft was, according to the captain's radio altimeter, flying too low. This happened several times during the approach to Schiphol. The reason that the captain's radio altimeter was causing problems was the first officer making a mistake when arming the aircraft's autopilot system for a dual channel approach.
> The Boeing 737NG type aircraft has two autopilot systems, which can work independently of each other (single channel) or together (dual channel). Turkish Airlines' standard operating procedure at the time stated that all approaches should be flown "dual channel" when available, but the inexperienced first officer forgot to arm approach mode in the aircraft's mode control panel (which controls the autopilot), meaning that the aircraft thought the pilots wanted to do a single-channel approach using control computer A (captain's autopilot), which had a radio altimeter failure.
[1] https://en.wikipedia.org/wiki/Turkish_Airlines_Flight_1951
[2] https://admiralcloudberg.medium.com/test-article-the-crash-o...
I note that the accident report on the Turkish airplane further confirms what we have since learned about Boeing:
* persistent issues with radar altimiters in the entire fleet
* issue classed 'low priority', even if it feeds into autothrottle
* near-crash results in 'fix' that disables autothrotle if two sensors disagree.
* 'fix' is not rolled out to the entire fleet. And it is not 100% effective.
* issue is not mentioned in documentation, pilots can not see which sensor is used
Is it me, or is this exactly the same history as MCAS? Drives home the famous mantra "if it's a Boeing, I'm not going"
He is very through and detailed, an instructor pilot with a lot of experience.
It is. And increasingly so in fact, as it allows more airports that don't have the resources to install and maintain ground-based equipment to have previously unavailable approaches. https://www.flyingmag.com/everything-you-need-to-know-about-...
However, it doesn't fall into exactly the same class as ILS approaches.
WAAS (GPS plus a correction signal transmitted by separate geostationary satellites) improves the resolution to CAT I standards - an "LPV" approach. However, it's still not sufficient for CAT II/III approaches.
A CAT III ILS approach requires very specialized equipment and training because you basically fly it all the way down to the runway with no requirement for visibility until moments before touchdown.
However, GPS is a lot better when it is not being obstructed by buildings around you. Planes have the benefit of unobstructed paths to GPS satellites and would get a better quality and accuracy then you might get with a phone in a city. Also, using good antennas helps. So, the altitude accuracy would be fine mostly.
I.e. the transmitter on the ground must be able to detect that something is wrong and immediately cut out the signal / report it as inop to the receiver on the plane. When you're seconds from hitting the ground, that is a requirement.
Although GPS based approaches have some aspects of this, I believe that they just don't meet the exact requirements as written currently, although they are close.
ICAO recognizes SBAS Cat I as a precision approach, and there are dozens of them in Europe (France, Austria at least).
In good conditions the approaches might be indistinguishable, especially given that GPS approach once on final will be usually a copy of GPS one, but the safety of GPS LPV is considered much lower, for a good reason.
See the following from gps.gov: it can be accurate to within centimeters and with a high polling rate, but most consumer devices don't employ the necessary tricks. https://www.gps.gov/systems/gps/performance/accuracy/
The highest resolution GPS receiver I have still has +/-15ns jitter, which over the course of a day is good enough for maybe 12-20cm resolution, but the first hour the track is wild, 50-80 meters off in varying directions.
My GPS is used as a time stamp source for lightning detection and location, so in aggregate with other detectors it can pinpoint a strike to within a meter or so anywhere in my hemisphere.
What misled you to think this? Radio altimeters are used throughout the aviation industry. Their ubiquity and criticality is the issue at hand. [0]
[0] https://www.faa.gov/other_visit/aviation_industry/airline_op...