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why should there be any element of risk in flying in a GA aircraft? |
Note I did not say "would". The word "should" was carefully selected.
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Inexperience??
Maybe the fact that so many GA pilots have so little flying experience these days.
I wonder how our major airlines would get on with 300 hour captains who moved on after a year or so, to be replaced by another newby. |
why should there be any element of risk in flying in a GA aircraft? Dr :8 |
Actually, the mention of reports reminded me of an early comment by Dick.
John Langmead, was violently opposed to me appearing. In a 10 minute “rant” to the Coroner, he came up with every possible legal technicality as to the reason I should not be allowed to appear. |
Steer clear of old GPS units
I had a "Trimble moment" on an IFR in IMC training flight a few days back, and thought I'd share the experience here for everyone's benefit:
Tracking YWE via Wendy to AV for the GPS Arrival, I was using the GNS-430 for distance and secondary tracking information while navigating primarily via the 430 VOR. My instructor was looking mostly at the Trimble in the right radio stack as it was right in front of him, and because I would switch modes and pages on the 430 every so often. About 15nm from AV, I decided to get the Centre air work and CTAF calls out of the way, when my instructor went: "That's a bit early, don't you think? We've got more than 40 miles to go to Avalon..!" :eek: And sure enough, the Trimble was showing 40-odd miles to AV. I double-checked the 430, all good, 15 nm to go, which was also in accordance with my flight/time planning. I then asked Centre for a position check to be sure, and they confirmed the information the 430 was giving me. We then proceeded to check the messages on the Trimble, and sure enough, there was the "No usable GPS data. Unit switched to dead reckoning mode." message.. :uhoh: The only indication something was amiss from the point of view of the Trimble was the small "MSG" light which of course also comes on in so many other circumstances.. :yuk: I knew about the Trimble trap from John Chew's excellent GPS course which I had attended some time back at MFT. He basically told us the Benalla story as a very vivid example of how things can go pear-shaped. Whatever the facts at Benalla, and setting aside for a moment that it's only 38 miles from YWE to AV :}, this goes to show that we must take every output from a machine with a healthy pinch of salt, and make sure we understand the workings and limitations of instruments we base (especially IFR) flight on. It's for a good reason that "man machine interface problems" are quoted as one of the prime causes for GPS related incidents and accidents! Now of course the Trimble is old and was designed at a time where concepts like "user interfaces" and "usability standards and practices" were in its infancy if that. And, let's face it, most pilots are no expert computer users, and are more attuned to steam gauges than complex multi page user interfaces, like those most aviation GPS units offer. It's oh so easy to have a rudimentary grasp of the basic function of any GPS, but when things start to go astray, the pucker factor often turns out to be inversely proportional to the time spent reading the GPS manual :8 Even with modern units like the GNS-430, I've easily managed to ignore the "GPS/VLOC" indication on the unit, and thus have tried to intercept a VOR track when the HSI was in fact showing me the GPS track divergence.. :eek: Another interesting point/trap is that the most common GNS-340 VOR/GS indicator GI-106 comes in two versions, one with (GI-106A) and one without in-built GPS/VLOC annunciator. In case of the latter, in most lighties, you will only have said "GPS/VLOC" indication on the GNS-430 display, and no indication what you're looking at on the indicator itself.. In this context, can I draw attention to the excellent Garmin 400/500 series simulators found here (Free 400/500 Series & GNS 480 Simulators), a great tool to play at leisure with all the functions, you can even "chair fly" upcoming test flights with them! As an aside, I can see why the FTDK flies with triple GPS redundancy. I personally am upgrading my Archer to a GNS-530, plus double VORs and ADFs, with a stand-by AirNav equipped (and backup battery powered) tablet PC running off a solar power GPS receiver.. I hope, once ASA get their act together and agree on the proposed ADS-B rollout, that I can eventually get traffic input via ADS-B IN on the display of the 530, and thus have an all-round solution to mitigate the most common flight risks. Safe flying everyone! |
In August this year I wrote to Minister Albanese to advise how professional pilot John Chew had found that the ATSB report (which stated that the GPS required manual inputs for it to fly in the dead reckoning mode) was wrong. I asked the Minister if he could request that both CASA and the ATSB inform pilots of this problem.
Amazingly enough, a reply came which in effect maintained the ATSB’s position – i.e. there is no need to tell pilots of this problem as a pilot should see the dead reckoning light! Here are the pertinent parts of the Minister’s letter back to me. The ATSB has advised me that it does not agree that its final report contained a ‘major error’ in relation to the dead reckoning operation of the GPS navigation receiver. The Bureau notes that, based on advice from the GPS manufacturer, the report stated: “During flight, operation of the receiver in the dead reckoning (DR) mode would occur when insufficient satellite signals were available for navigation. A message would alert the pilot to the dead reckoning mode of operation and require groundspeed and track to be manually entered. …” The ATSB is currently engaged on this matter with the GPS manufacturer, which has advised that further testing is required to confirm the interaction between the aircraft’s air data computer and the GPS unit. The ATSB also notes that its report did not state that the receiver would provide navigation guidance for tracking a GPS approach in dead reckoning because the ATSB considered that the GPS receiver would alert the pilot through messages and warnings, as required by certification. I am advised by the Civil Aviation Safety Authority (CASA) that it also considers that the messages and warnings available to the pilot should have provided him with enough information about the status of the GPS receiver. As you may be aware, the ATSB reopened its investigation into this accident on 22 July 2008 to consider the information provided by Mr Chew about a GPS approach with the receiver navigating in the dead reckoning mode. It found that, while this was possible, the demonstration was not flown using the same parameters as the accident flight and therefore could not claim, as you assert, to “…replicate exactly the approach made by the accident aircraft”. The ATSB found that a number of assumptions had been made in the demonstration to explain how a pilot could ignore the numerous GPS messages designed to alert pilots to invalid navigation information. Those assumptions were not substantiated and the ATSB is unable to conclude positively that the GPS receiver in the accident aircraft was navigating in dead reckoning mode. The ATSB is continuing its reopened investigation of this matter, including liaison with the receiver’s US manufacturer. If any safety issues arise the ATSB will amend its report and, if necessary, add to its findings and safety actions. I am advised that CASA is considering the issues raised by the ATSB and monitoring the reopened investigation. I can assure you that once the reopened investigation has been completed, both the ATSB and CASA will take appropriate action to ensure aviation safety is maintained. |
Demo/practise mode??
I remember sitting in a avionics workshop in Parafield for a couple of days "flying" a unit that was on the bench, operating in Demo mode, while they were fitting one to our aircraft. It did everything that would normally happen in flight.
That may heve been Omega, or Trimble GPS. We used both. I think it may be possible that something like this may have happened to the Benalla aircraft, and this should definitely be checked. There is a reason why the aircraft crashed near Benalla. |
Excellent post Plankblender - I don't know how I missed it until now!
It's oh so easy to have a rudimentary grasp of the basic function of any GPS, but when things start to go astray, the pucker factor often turns out to be inversely proportional to the time spent reading the GPS manual http://static.pprune.org/images/smilies/nerd.gif The last time I flew a long X-country flight (Townsville-Toowoomba) the G430W in the FTDK flicked into DEAD RECKONING MODE twice. I had never seen this before and assume it was related to the TSO146a specs (the other two non-TSO units carried on quite happily!). I need to go read the book some more. The first time caught me by surprise somewhat. It stayed that way for several minutes and in the end I got pissed with it and did a re-boot - came up fine. The second time I dived for the digital camera that I carry in the side pocket to record the moment for Ppr**ne Photos, but by the time I had the camera out it had returned to normal. I personally am upgrading my Archer to a GNS-530, plus double VORs and ADFs, with a stand-by AirNav equipped (and backup battery powered) tablet PC running off a solar power GPS receiver Dr :8 |
The last few posts hit the nail on the head for many pilots these days. RTFM and know something about your equipment. The fact that the trimble comes up with a message, that it was in DR mode, simply point out the fact that if you are going to use the equipment, include it in your scan - all the time! Yes the MSG light on the trimble is small, all the more reason to look at it from time to time. The reality is you covered some 25 miles or more in DR mode before you looked at and checked the message. The question then is "how come?"
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What about RAIM?
I dunno about you guys but I have always been taught to go into the GPS unit and check that RAIM is available prior to TOD. Surely if this had been done in the Trimble accident the operator would have been alerted to the D/R mode?????
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Grogmonster,
What you are saying regarding RAIM is quite correct, although on a number of occasions I have been on an NPA approach with sat coverage calculated OK by both the GPS unit and the NAIPS website, but, on approach the GPS loses coverage, a good proportion of these times it has been in mod icing / relative high humidity, go figure..... |
My two cent's worth
Trimble has all messages and warnings as far as operatinal requirements go, perhaps not some of the fancy stuff that some of the new gear has Perhaps it depends on the setup and how it's interfaced, although the display window is small and the msg light is like a star in the distance, they can be arranged to make aural warnings and can be fed through the intercom system...you know the beep beep.....and the display shows the warning too on pressing the message button to make the beep go away, this can be position approach transitions, RAIM alerts, fuel warnings (if totaliser interfaced), enable approach to feed QNH etc.,i've come across the aural warning not working (or too quiet) and it took a cone head few minutes to fix it, obviously its a maintenance side with entering into setup mode etc etc, perhaps if there's a cone head around here can explain a tad more For another question earlier in the postings....I would say the approach can be still loaded if the data card is out of date...... will have to check on this one for I've never had a Trimble out of date I find it interesting on the comment that an unplugged or failed aerial could do this....please provide source of information !! or was it your backyard cookup :? Smoothie :ok: |
I find it interesting on the comment that an unplugged or failed aerial could do this....please provide source of information !! or was it your backyard cookup :? J |
LHRT,
a good proportion of these times it has been in mod icing / relative high humidity, go figure..... |
You should phone the ATSB and offer your observations. Stranger things have happened before!
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Smoothie, you state:
I find it interesting on the comment that an unplugged or failed aerial could do this....please provide source of information !! or was it your backyard cookup :? |
Thanks Dick, appreciate the link
Smoothie :ok: |
Coroners Court - Victoria
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