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Timmy Tomkins
My hunch is that they were on the OIFM ASR radar until 60 miles south of OIFM. But, that is still 80 miles north of OISY. I don't know whether Iran has long-range center radar covering the area between OIFM and OISY. If so, the minimum altitude of center radar coverage would likely be fairly high in the vicinity of OISY. |
Thanks for the informative response; I suspect you are right.
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GPWS has geometric height input signal (no barometric). RA don't work in this range. I suppose they is used data abt height from GPS. In South Iran, I hope, can receive EGNOS from sattelite IOR 64 East. ATR-72 was below glideslope abt 30 metres and runway close abt 120 metres.
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AvHerald has updated their info on this crash.
Crash: Iran Aseman AT72 near Semirom on Feb 18th 2018, impacted terrain The following picture from AvHerald shows that they never reached the Yasuj NDB to begin the approach. I imagine the CVR will be able to provide some clues as to what they were thinking/seeing. http://avherald.com/img/aseman_at72_...80218_map4.jpg |
Originally Posted by Machinbird
(Post 10069559)
AvHerald has updated their info on this crash.
Crash: Iran Aseman AT72 near Semirom on Feb 18th 2018, impacted terrain The following picture from AvHerald shows that they never reached the Yasuj NDB to begin the approach. I imagine the CVR will be able to provide some clues as to what they were thinking/seeing. http://avherald.com/img/aseman_at72_...80218_map4.jpg I hope Iran lets us all know in due course. As I recall, they do a very good job of accident investigation, with subsequent disclosure in accordance with ICAO protocol. Perhaps TRW that were quite cold at the flight's altitude, which could result in a lot of ice in addition to turbulence. RIP |
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In the absence of visibility, they apparently went in to land on the GPS.
What are the "underwater" stones when entering GPS? 1. Is it known exactly which ellipsoid (datum) is used in the country?? (page 6 of manual GNS430) 2. Whether the reception of differential corrections (WAAS, EGNOS, etc.) is reliable?. Maybe I'm wrong, but it turns out this picture: - if the GPS is operating in diffrent mode (2 in field 6) sentence $GPGGA, the GPS will ignore the incoming altitude from the barometer and will take the height of the GPS, as more accurate. - What is the height of the GPS? This is the distance to the satellites. - then "roll" the desired geoid / ellipsoid and get a height above the terrain. A similar catastrophe was in Colombia on November 28, 2016 RJ-85, there in the airport area the WAAS system operates. |
The crash site is about 4 miles from the airway centerline.
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Double Back
"Flying any non-precision in a heavy jet is outright dangerous" What complete cobblers , cant speak for Mr Boeings but with Mrs Airbus , any NPA is a delight , very similar to an ILS , yes certain traps and gotchas but "downright dangerous , rubbish . If you are briefing an emergency for a simple manoeuvre that is easy to brief and fly , you are in the wrong job . |
Re #64/67. The information appears to relate to Airbus aircraft which may use an alternative form of TAWS/GPWS.
Was this aircraft fitted with TAWS or EGPWS? Did this aircraft have an external GPS (Nav). Was this connected to EGPWS, or did the aircraft only have a GPS receiver within EGPWS (no Nav), or none at all? What is the resolution of the EGPWS terrain data base in this area, similarly for the airfield. If the airport was not fully covered then basic GPWS should still be available - subject to switching / selection. Rad Alt will display altitude according to scale, normally at any time less than 2500ft agl. (E)GPWS will use this, and thus if serviceable there should at least have been a basic GPWS alert / warning. IIRC ATR had a history with GPWS inhibit switching, it could be completely switched off to inhibit nuisance alerts (fatal accident, ... Taipei ??) . Is similar switching used for EGPWS, or is there the more conventional selection of terrain off - leaving the basic system active? |
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Originally Posted by PEI_3721
(Post 10072636)
Re #64/67. The information appears to relate to Airbus aircraft which may use an alternative form of TAWS/GPWS.
Was this aircraft fitted with TAWS or EGPWS? Did this aircraft have an external GPS (Nav). Was this connected to EGPWS, or did the aircraft only have a GPS receiver within EGPWS (no Nav), or none at all? What is the resolution of the EGPWS terrain data base in this area, similarly for the airfield. If the airport was not fully covered then basic GPWS should still be available - subject to switching / selection. Rad Alt will display altitude according to scale, normally at any time less than 2500ft agl. (E)GPWS will use this, and thus if serviceable there should at least have been a basic GPWS alert / warning. IIRC ATR had a history with GPWS inhibit switching, it could be completely switched off to inhibit nuisance alerts (fatal accident, ... Taipei ??) . Is similar switching used for EGPWS, or is there the more conventional selection of terrain off - leaving the basic system active? I don't know, what kind of navigation equipment was installed on this airctaft. GPS, probably, is HT-1000. RadioAltimeter can't work in this case - out of range ( abt 1500 m). |
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HT-1000 GPS.
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Patanom, I disagree with your views of rad alt.
If the aircraft hit a hill then the rad alt was 0ft. Thus for flight preceding that, at some time the altitude would have been between 0ft and 2500ft. RA input to the basic GPWS would have warned according to terrain rise and aircraft descent rate; whether the aircraft could be recovered would depend on the time available according to terrain profile and crew reaction. If EGPWS was working then earlier alerts would have been given so that a recovery manoeuvre should not be in doubt ... except for ... Local research suggest that the 212 version of the aircraft would have been fitted with EGPWS vice a Thales alternative, although the latter is now standard. Previous EGPWS accident in ATR 42 Crash: Trigana AT42 enroute on Aug 16th 2015, aircraft collided with terrain |
Rare situation - treat as per emergency?
Double Back and Nil further,
My intent is not to fan a disagreement, but your exchange prompts me to ponder whether or not it is valuable for a flight deck crew to treat (at least within the cockpit) any situation that they rarely experience as if it were an emergency. It seems to me that there is high value in elevating the attention to details for everyone involved if the task at hand is one that is not common and has the potential to go south in a hurry if not done properly. I am not suggesting that every time a crew encounters a situation that they have not seen in the last six months that they declare an emergency to ATC and make cabin announcements that would overly worry their passengers. What I am finding re-assuring as one who is in the airplane design end of the business and whose flying experience is about half as a test engineer in the back and half as SLF is that the folks at the front end take their safety job seriously and do their best to earn my trust and their pay. This is particularly the case when conditions lead to a combination of events not typically encountered. Another part of my thinking on this is that with real emergencies so few and far between these days it seems valuable to me to have crews practice for the eventual bad day by treating a few less than perfect days as if they had the potential to become real "remember when" stories for pub visits deep into the future. My deepest respect for all aircrews who spend their time up front anticipating and preparing for the day when they may earn a career's worth of respect over the course of just a few minutes or hours. |
Aircraft configuration changes alter GPWS responses. I recall A320 GPWS from many years ago where gear down at less than 1800ft/min rad alt closure rate to terrain would give "too low flap". This alert would be more typically found during a constant altitude flight during a circling approach over high ground outside the circling area with less than landing flap. Same result could be expected if other minimum altitudes or defined tracking are not respected with gear down.
I am confident that more than a few readers would find this safety warning limitation of GPWS surprising. At some time the GPWS has to recognise that the intent is to land and this seems to be a transition from normal full flight capability to actual touchdown conditions. I accepted that there is a transition risk. Unless there have been other mode changes since, the reduced warning capacity needs consideration. |
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PEI 3721, I agree, that EGPWS has to work accordance with this algoritm. But....
Two signals are sent at the input to the Geometric Height, - the radio altimeter and GPS. I suppouse, that in this region there was a reception of differential corrections (WAAS or other) through the geostationary satellite POR 140 degrees. In this case GPS altitude will be used. In database of EGPWS is WGS-84, but in this region the Indonesian datum is used and the height difference is 22.99 meters. Those. the EGPWS system considered a different relief than the actual one. I suppose that with the ATR-72 the same situation (the difference in altitude is 30 meters) |
From AvHerald: On Mar 11th 2018 Iran's AIB released their preliminary report in Persian reporting that according to FDR and CVR the aircraft had been handed over to Yasuj Tower, the autopilot was set to 15,000 feet. Descending through 15,600 feet the crew activated the anti-ice systems. The aircraft levelled off at 15,000 feet on autopilot, the crew set the QNH to 1021 and maintained 15000 feet for about one minute. Then the engines were reduced to idle, the speed reduced to 200 KIAS with the angle of attack increasing, the engines get slightly accelerated. The speed continued to decrease and reached 129 KIAS (minimum maneouvering speed 132 KIAS), the pitch reaches 15 degrees nose up, the engines accelerate to 67% torque. The altitude target is set to 14,000 feet and the aircraft begins to descend at about 600fpm. The speed further reduces to 117 KIAS, a stall warning activates, the crew disengages the autopilot, the aircraft rolls 20 degrees to the left, the pitch reduces to about 9 degrees nose down. Descending through 14200 feet at 137 KIAS the autopilot gets re-engaged, the aircraft rolls right by 12 degrees, the pitch increases to 5 degrees nose down. A GPWS warning "TERRAIN AHEAD! PULL UP!" activates, the autopilot is disengaged, the GPWS warning continues for 12 seconds until impact. The AIB continued that there was no technical malfunction of the aircraft, the engines operated in accordance to pilot inputs, all aircraft systems supplied the crew with valid data. Due to the cloud cover the crew remained unaware of the mountains ahead until 2 seconds before impact and rolled the aircraft sharply left in order to avoid the terrain. The AIB stated that the crew should have maintained 17,000 feet in accordance with the flight plan, however, descended the aircraft to 15,000 feet followed by a target altitude of 14,000 feet on the autopilot contrary to flight rules. In addition, while the crew was permitted to conduct the flight with the weather data available at the time of departure, the latest weather information provided by Yasuj Tower indicating clouds up to 15,000 feet prohibited the approach to Yasuj according to company procedures due to cloud cover present at the aerodrome, the crew should have diverted to Shiraz or Isfahan planned as alternate aerodromes. Pilot discussions according to the CVR confirm the presence of cloud up to 15,000 feet confirming the accuracy of the weather report by Yasuj Tower. Although the aerodrome was still more than 10km away the crew appeared to be confident the area would be in visual meteorologic conditions. The AIB warns that all of this is first interpretation of first investigation results and is not to be taken as cause of the accident. |
It turns out a pilot error, but why?
According to the report, it was allowed to reduce the altitude to 17,000 feet, but the pilot initially set the altitude of 15,000 feet on the AP, and then set the altitude to 14,000 feet. Everything, including engines and anti-icing systems, worked fine, and a technical problem was not noticed. The pilot at 9:31:14 received a warning from GPWS. From another forum: Interesting decision to re-engage the autopilot following a stall. Not necessarily a turning point in the sequence of events. I'm assuming the momentum of 67% from that point on? I believe around low 70's is a normal cruise power for those altitudes in that aircraft. Certainly reads like there was a major breakdown in situational awareness in the flight deck. Ignoring a GPWS for 12 seconds is puzzling. Language barrier? Startle effect? Poor training? Final (?) report, but not yet translated into English ... http://www.mizanonline.com/files/fa/...555079_507.pdf |
The minimum altitude on the airway is 17,000. But, they could have elected 15,500 when within the north MSA sector. However, they were almost 4 miles off course, which is a significant navigation deviation and an unsafe location from which to begin the instrument approach.
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