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But why would you want to "level off" at MDA?? I'm not trying to be flippant here, and I understand that on a continuous descent approach you wouldn't have leveling off at MDA as a part of your planned profile. But apparently, at some point they descended thru MDA. I understand that there are a whole lot of unanswered questions at this point. But consider the possibility that a greater awareness of MDA and a greater awareness of exactly what conditions should exist before descending below MDA might have prevented this accident. |
Setting the MDA in the altitude window has been implicated in a couple of incidents. While is seems sensible to the dive-and-drive camp, a pilot would not desire the aircraft to level during a constant-angle approach. It would only serve to unstabilise the descent. The AP would have to be taken out and descent re-initated to the runway which could lead to a long landing.
The CANPA method requires the missed approach altitude to be set before starting the final descent to "unlock" the altitude hold. If that altitude happens to be the same as platform, our procedures require setting 100' above platform until the descent has begun, then reset to the missed approach alt. shortly thereafter. It requires deliberate action and thinking by a crew to get it right. It's an NPA, after all. |
Question for Aterpster
Sir,
Why would an approach (like LOC 18) have the minimums be NA for night only? Does that imply some terrain issues between MDA/DDA and the TDZ? BTW, I can't believe you are still actively involved in this work! Thanks for your contributions both to the industry and to educating all of us over the internet for 'lo these many years'! |
Originally Posted by FIresysok
While is seems sensible to the dive-and-drive camp, a pilot would not desire the aircraft to level during a constant-angle approach. It would only serve to unstabilise the descent. The AP would have to be taken out and descent re-initated to the runway which could lead to a long landing.
That said, why not set MDA in the alerter on a CANPA? You add 50' to the MDA for a pseudo DA, right? (surely you don't use MDA as a DA with the inevitable descent below?) So, if you arrive at MDA, then one of two things have happened. You've reached MDA + 50, didn't see the runway and have already initiated the missed approach. Or You've reached MDA + 50, have the runway environment in sight, and are continuing the approach with the auto pilot disengaged. (At my airline, we don't continue below MDA on the autopilot, is this done at other airlines? ) So ..... hypothetically, if a Crew was so focused on following their VNAV cue that they missed the fact that they were descending through MDA wouldn't the autopilit pitching up to capture tthe MDA be a nice handy reminder to not descend below MDA? |
Setting the MDA in the altitude window has been implicated in a couple of incidents. While is seems sensible to the dive-and-drive camp, a pilot would not desire the aircraft to level during a constant-angle approach. It would only serve to unstabilise the descent. The AP would have to be taken out and descent re-initated to the runway which could lead to a long landing. |
So, if you arrive at MDA, then one of two things have happened. You've reached MDA + 50 and have already initiated the missed approach. Or You've reached MDA + 50, have the runway environment in sight, and are continuing the approach with the auto pilot disengaged. (At my airline, we don't continue below MDA on the autopilot, is this done at other airlines? ) In the above scenario, you legally cannot descend below 100' above TDZE unless the runway environs are in sight. If the AP has already started to round out the descent at MDA, the airplane will no longer be "stable", and you've given up the approach. All that said, if you're continuing down a NPA based on approach lights alone, you are already rolling the dice IMO. Because it's allowed by regulation, my company has decided to give the option to pilots. Whether or not it is good practice in reality is another discussion. Approach lights that extend out far enough to be seen at non-precision MDAs would most likely be installed on a precision runway. Those lighting installations provide good roll reference; vertical reference not so much. I can see the above scenario working well to a precision runway with G/S out. An approach to 18 at BHM or most other NP runways, it would not come into play more than likely. |
A question for anyone with a better understanding of the actual equipment installed in this airplane.
In the avionics suite installed in my airplane, we have the ability to set the MDA/DA separately from the altitude in the altitude alerter window. This does two things: It superimposes a MDA line on the altitude tape, and it triggers two aural alert, "approaching minimums" and "minimums". I don't see any mention of similar alerts in the NTSB briefing one the CVR, but of course it's not a complete transcript. Would the system installed in the accident airplane have a similar capability, and would you expect similar aural alerts approaching and reaching MDA? |
You've forgotten one scenario. In my company (also allowed by FAA), we are permitted to descend below MDA with *only* approach lights as reference, but *only* if the plane is in a position to continue a stabliised descent to the runway. (with AP disengaged) In the above scenario, you legally cannot descend below 100' above TDZE unless the runway environs are in sight. If the AP has already started to round out the descent at MDA, the airplane will no longer be "stable", and you've given up the approach. One minor correction: You're allowed to descend to 100 ft lower than MDA, not down to TDZE + 100. I realize that on a standard Cat I ILS these are the same, but this is in the context of a NPA. I guess I'm not following your how descending on the lights is different. Presumably on a CANPA, you would have the lights in sight (but not the runway) at MDA + 50 or you would have initiated the Missed Approach. If you're descending below MDA, the presumably you had lights in sight 50 feet prior and have already made the decision to continue below MDA and disengaged the A/P. I'm not seeing where having MDA set in the altitude alerter would affect either of those scenarios. And yes, I agree that descending below MDA on the lights alone is rolling the dice. |
Quote: But why would you want to "level off" at MDA?? When you don't have the field in sight... NoD |
That said, why not set MDA in the alerter on a CANPA? You add 50' to the MDA for a pseudo DA, right? (surely you don't use MDA as a DA with the inevitable descent below?) |
Check FAR 91.175:
[(c) Operation below DH or MDA. Except as provided in paragraph (l) of this section, where a DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, at any airport below the authorized MDA or continue an approach below the authorized DH unless-- ] (1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing; (2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and (3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot: (i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable. (ii) The threshold. (iii) The threshold markings. (iv) The threshold lights. (v) The runway end identifier lights. (vi) The visual approach slope indicator. (vii) The touchdown zone or touchdown zone markings. (viii) The touchdown zone lights. (ix) The runway or runway markings. (x) The runway lights. [(d) Landing. No pilot operating an aircraft, except a military aircraft of the United States, may land that aircraft when-- (1) For operations conducted under paragraph (l) of this section, the requirements of (l)(4) of this section are not met; or (2) For all other part 91 operations and parts 121, 125, 129, and 135 operations, the flight visibility is less than the visibility prescribed in the standard instrument approach procedure being used. Let's say the MDA is 500' baro. Add 50' for a new DDA of 550' baro. Unless you can set 550' in your altitude alerter, you would have to round up to 600', giving up another 50'. If your AP starts the altitude capture at say....around 650' baro, you've now given up *another* 50' and committed yourself to a missed approach. In our airline, the pilot monitoring would call "minimum, approach lights/runway in sight" at 550' on the altitude tape, PF would disconnect, (the airplane still trimmed and descending), and you would continue manually to the runway. I'm not understanding why an an autopilot-controlled level-off would be beneficial to any crew using CANPA procedures other than to make arses and elbows out of an already complex procedure. |
Originally Posted by Nigelondraft
In all my airliner flying, if you don't have the field in sight at MDA you Go Around, not level off. I accept other operators / nations may differ...
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Firesysok, I stand corrected on the descent with the lights. Thanks. gues I didn't remember that as well as I thought I did.
I see your point about the MDA if the SOP is to set the "adjusted" MDA (MDA + 50, rounded up to the next 100') My commens were based on the assumption that you're set the actual published MDA in the alerter, and would have either decided to continue or decided to miss prior to having reached the MDA. |
Originally Posted by Dream Land
First of all, there is no need to add 50 ft to MDA, at least our Feds did away with that years ago,
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The 50' addition to MDA is for CANPA-type procedures only.
In a dive-and-drive procedure it is not needed because the aircraft is already level. In a constant-descent procedure it is needed because of the inertia of an airplane already in descent. It ensures the crew can "round out" the descent when executing a missed approach and not descend below the published MDA. |
pipeliner:
Sir, Why would an approach (like LOC 18) have the minimums be NA for night only? Does that imply some terrain issues between MDA/DDA and the TDZ? http://aeronav.faa.gov/d-tpp/1308/00050L18.PDF BTW, I can't believe you are still actively involved in this work! Thanks for your contributions both to the industry and to educating all of us over the internet for 'lo these many years'! |
I interpreted that not to mean "level off" exactly, but more : Not continue descending . .. . which you would be doing if you were initiating the missed approach. |
Something from the CVR is puzzling me.
At end of recording -16 seconds, we have the sink rate warnings. At EOR -13 seconds, one of the crew remarks "Runway in sight". Why was that call made? Based on the weather, the runway should have been visible well before this. Was this call for FOQUA reasons? Is it indicative of an "OPS Normal" mindset? Just seems out of place in the context of 4 seconds before impact with the trees. |
JAN-W iNPA approaches are 'safe' but an RNAV RNP AR approach to RNP 0.1 is safer that is why when flying them you have lower limits. If you are talking about preferences, that's a different story, but it has nothing to do with safety. If you are talking about various degrees of proficiency to fly NP approaches for individual crews, that might be the elephant in the room. You are right, this discussion comes up with accidents like this one and Asiana in SFO, but i dont see the conection between the type of approach flown and the fact, that the aircraft ended with a CFIT short of the runway after droping well below glidepath and like in SFO being well below Vref. In any approach there are min altitudes, min airspeeds and established procedures involved, some of those have been written in blood over the years. "Stabilized approach criteria and CRM " come into mind. You deviate from those, and you have a good chance to hit the news some day regardless wether you fly an ILS or a NDB / V approach. |
Something from the CVR is puzzling me. At end of recording -16 seconds, we have the sink rate warnings. At EOR -13 seconds, one of the crew remarks "Runway in sight". Why was that call made? Based on the weather, the runway should have been visible well before this. Was this call for FOQUA reasons? Is it indicative of an "OPS Normal" mindset? Just seems out of place in the context of 4 seconds before impact with the trees. |
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