Airline Pilot Forums

Airline Pilot Forums was designed to be a community where working airline pilots can share ideas and information about the aviation field. In the forum you will find information about major and regional airline carriers, career training, interview and job seeker help, finance, and living the airline pilot lifestyle.




View Full Version : Autopilot level-off at MDA


foumanchu
11-14-2018, 12:24 PM
If you are doing the traditional "Dive and Drive" method on a non-precision approach with the Autopilot Coupled, i.e. VS Mode, does any plane/company require an additive to the MDA due to the tolerances of the Autopilot capture/hold capabilities?


Adlerdriver
11-14-2018, 12:41 PM
I don't believe I saw any used due to autopilot limitations (737, 757/767, A320, MD-11), 3 airlines. If you could enter the exact MDA into the automation, that's what you used.

galaxy flyer
11-14-2018, 01:02 PM
Altimeter error, along with nav instrument errors are all part of the Flight Technical Error Budget, just set the MDA and go for it.


Gf


foumanchu
11-14-2018, 01:08 PM
I don't believe I saw any used due to autopilot limitations (737, 757/767, A320, MD-11), 3 airlines. If you could enter the exact MDA into the automation, that's what you used.

Thanks for perspective.

I wouldn't think that you would have to, but I ran into a "technique" (not sure that it is driven by any credible technical data) for specific plane that has that.

Hope more chime in to see if anyone at all does it.

PerfInit
11-14-2018, 05:30 PM
Most operators “round up” to the next 100ft increment.

Adlerdriver
11-14-2018, 05:37 PM
Most operators “round up” to the next 100ft increment. Every glass airplane I've flown had the ability to put in the exact MDA (or at least rounded to 10 feet) and the autopilot would level off there. So, I don't think it's a very accurate statement to say "most operators round up to the nearest 100 feet". Some do, many don't.

The other thing to consider is, in 2018, I would say that "most operators" aren't doing dive and drive approaches any longer.

zondaracer
11-14-2018, 06:09 PM
On the CRJ, the MDA can select the MDA and it rounds to the nearest 10 feet, but the altitude selector in the autopilot has to be rounded up to the nearest 100 feet.

Adlerdriver
11-14-2018, 06:26 PM
On the CRJ, the MDA can select the MDA and it rounds to the nearest 10 feet, but the altitude selector in the autopilot has to be rounded up to the nearest 100 feet.Does your company still train to do dive and drive?

zondaracer
11-14-2018, 06:51 PM
Does your company still train to do dive and drive?

No, constant angle non precision approach. Add 50ft to the MDA. There are some approaches that require a dive and drive such as the LOC/DME 15 in Aspen.

JamesNoBrakes
11-14-2018, 08:15 PM
Thanks for perspective.

I wouldn't think that you would have to, but I ran into a "technique" (not sure that it is driven by any credible technical data) for specific plane that has that.

Hope more chime in to see if anyone at all does it.

The POH/AFM/Autopilot supplement will state what the limits are for the autopilot, in other words, what you can use it for. if it says you can go down to MDA or DH, you can do exactly that. If there are any quirky limitations, they'll be stated.

foumanchu
11-14-2018, 09:56 PM
The POH/AFM/Autopilot supplement will state what the limits are for the autopilot, in other words, what you can use it for. if it says you can go down to MDA or DH, you can do exactly that. If there are any quirky limitations, they'll be stated.

The only thing I can find is the autopilot is capable of maintaining altitude in ALTS mode with an overshoot of less than 40 ft.

I would think that every autopilot has some kind of overshoot tolerance and that is still acceptable when using ALTS to capture the MDA.

I have a feeling that the technique in question started from someone that is confusing adding in a buffer like you would to get a DDA on CDFA type profile. That of course is to allow for the decision to continue or go-around on a non-precision like you would for a precision approach.

galaxy flyer
11-15-2018, 06:45 AM
Does your company still train to do dive and drive?

Do you fly constant angle to circling approaches? :cool: Yes, you don’t fly circling approaches, but others do.

GF

Adlerdriver
11-15-2018, 09:20 AM
Do you fly constant angle to circling approaches? :cool: Yes, you don’t fly circling approaches, but others do.

GFI’m not sure what you’re trying to say to me GF.

zondaracer
11-15-2018, 12:06 PM
Does your company still train to do dive and drive?

We also do a dive and drive to a circling maneuver (VMC only of course).

galaxy flyer
11-15-2018, 12:51 PM
I’m not sure what you’re trying to say to me GF.

Bit of a jab in that circling is the only place “dive and drive” (dive to MDA, ALT CAP, drive to visual) might be useful, but airlines don’t circle.

GF

Adlerdriver
11-15-2018, 01:30 PM
Bit of a jab in that circling is the only place “dive and drive” (dive to MDA, ALT CAP, drive to visual) might be useful, but airlines don’t circle.

GF
Okay - this thread has veered of topic a bit, probably in part due to me.

We started with "does anyone buffer MDA due to autopilot limits". When someone offered a blanket statement about rounding, I countered but unfortunately used a blanket statement of my own.

After that, I was truly asking if zondaracer's company still trained for D&D out of pure curiosity because maybe it's not as uncommon as I thought. I'm pretty sure it's been at least 8 years for me personally since I did a D&D in the sim. Last one I did real world was probably 15 years ago into SAN.

Now we're talking about circling approaches....Okay. A much, much smaller subset of the non-precision approach referenced by the OP. But, why not?

IMO, they are pretty rarely used unless there isn't any other choice. Why would anyone do that if there's a straight in type approach available to the runway they want to land on?
Unless my iPad doesn't show all the Aspen approaches, it looks like circling is your only option if you have to shoot an approach. I think we all can agree that's pretty unusual. I'm sure there are other fields like that, but my guess is that most airline pilots (vs. 91 types) aren't going to find themselves flying into that many fields where circling is the only way to get in. But if your 121 outfit or corporate flight department services a field like that, then I guess you're still going to train to D&D.

It looks like United and Delta both service KASE, so wouldn't that make them (or the sub-contractors that actually fly into ASE) airlines that actually do circle?

I can't imagine why anyone would fly a constant angle approach to a circle... wouldn't that just make the whole thing more difficult, possibly get tight and have to miss? It seems like getting down, getting visual and setting up the final approach would be the better option, especially if you're flying the approach to a different runway than the one on which you intend to land.

galaxy flyer
11-15-2018, 01:41 PM
Adlerdriver,

When the “dive and drive” mention, I had flashbacks to the JFK 04L or R VOR approach, circle to 31R in the Global sim profile. I did that damned thing dozens of times in initials and recurrent. The briefing was all questions, like; “describe D&D, how to set up the panel, what ALTS settings, how to circle?” At first, interesting, later, not so much. The circle to 29 at EWR was a change that was a challenge, then the circle to MEM was pretty simple, lots of airport to look at.

ASE is interesting, alright, but if I had the slightest doubts, it was off to Rifle.

GF

zondaracer
11-15-2018, 02:45 PM
It looks like United and Delta both service KASE, so wouldn't that make them (or the sub-contractors that actually fly into ASE) airlines that actually do circle?



SkyWest does all the flights for United, Delta, and American into KASE, and there is an approach with a straight in MDA that won't show up in your plates unless you have special authorization.

We also fly into KPSP, and the CRJ guys only have a VOR/GPS approach with circling minimums as an option. The E175 guys have an RNP approach that they can use. We have a couple airports like this.

Adlerdriver
11-15-2018, 03:28 PM
We also fly into KPSP, and the CRJ guys only have a VOR/GPS approach with circling minimums as an option.
Due to equipment limitations with that particular a/c?
Do you know how they fly that VOR approach?

zondaracer
11-15-2018, 03:45 PM
Due to equipment limitations with that particular a/c?
Do you know how they fly that VOR approach?

http://155.178.201.160/d-tpp/1812/00545VGB.PDF

It's a dive and drive with a visual maneuver to land. You can do it either VOR or with the GPS. The CRJs at SkyWest are not RNP0.3 approved.

I read that you can get a CRJ approved for RNP approaches with the correct dual FMS hardware and software, but not all of our CRJs have dual FMS (at least not yet), and I don't even know if it is the approved FMS that is being installed for the capability.

threeighteen
11-15-2018, 03:48 PM
Due to equipment limitations with that particular a/c?
Do you know how they fly that VOR approach?

SkyWest CRJ is not RNP capable, so the only option is VOR or a GPS over-lay of it. Minimums for it are pretty high at 2300' MSL (1823 HAT), so 2300 would be spun into the ALT SEL. If the Minimums were 2305, 2305 would be set in the MDA window, but 2400 would be spun into the ALT SEL and the AutoPilot/FD would level-off there. One could hand-fly down to 2305 if desired. With the autopilot on, the CRJ will level off above the minimums since the AutoPilot/FD can't be programmed to level off at an altitude that doesn't end in "00."

Adlerdriver
11-15-2018, 04:42 PM
Okay - thank you both.
A better follow up from me would be would they fly a VOR approach (with straight-in mins) like say, VOR 26L/R (KLAS) or LOC 27 (KSAN) differently than that circling VOR in PSP?
i.e. Different altitude selected in ALT SEL, Different vertical mode, procedures, etc.


Or is this all moot because we're talking about an aircraft that doesn't have VNAV, PROF or whatever someone wants to call the ability to program a vertical path?

zondaracer
11-15-2018, 04:50 PM
For straight in minimums on a VOR/LOC/VNAV approach, we will add 50 feet to the MDA and we call this the derived MDA. Prior to the final approach point, we calculate the descent rate based on ground speed and the descent angle. At the final approach point, we descend at that calculated descent rate and execute a missed at the derived MDA. The momentum should take you no lower than the MDA on the missed (thanks to the 50’ buffer).

The CRJ does have advisory VNAV and will display a calculated descent path but this is for situational awareness only, and it is only available with an RNAV approach or if you are using the GPS overlay.

Adlerdriver
11-15-2018, 06:35 PM
For straight in minimums on a VOR/LOC/VNAV approach, we will add 50 feet to the MDA and we call this the derived MDA. Prior to the final approach point, we calculate the descent rate based on ground speed and the descent angle. At the final approach point, we descend at that calculated descent rate and execute a missed at the derived MDA. The momentum should take you no lower than the MDA on the missed (thanks to the 50’ buffer).

The CRJ does have advisory VNAV and will display a calculated descent path but this is for situational awareness only, and it is only available with an RNAV approach or if you are using the GPS overlay.
Yes, we call it a Derived DA - DDA (since we use it like a DA). We can use published MDA as a DA without the 50 ft buffer in a few specific cases. One being LOC approach with G/S OTS - as opposed to having no published ILS and just a LOC.

Another question - sorry, just being a geek tonight: It sounds like you're coming down in V/S or maybe FPA as you approach the derived MDA. Is that what you have in the ALT SEL? In other words, if you do nothing approaching that altitude, will the a/c level off at mins or continue down toward the runway?

I ask because when we used to do something similar in the MD-11, it would level at mins. The problem was, since you were already basically on glide path, if you let it start leveling off, unless you reacted almost immediately, it was going to be very difficult to get it back onto glide path. So, if you had to go right to mins to break out, you needed to disconnect the A/P no later than 200' prior to the DDA so you could stay on glidepath. Now on the 777 (and I think they changed on the MD too), you put runway elevation in the ALT SEL window so it keeps going down and you have to intervene to go missed (like an ILS) which makes much more sense since you're using a DA just like an ILS.

zondaracer
11-15-2018, 06:52 PM
We descend in VS mode, and in the altitude select we have the missed approach altitude set. At the derived MDA, if we go missed, we disconnect the autopilot and fly the missed. If we continue to land, we disconnect and the plane is usually trimmed out to continue down the descent path.

foumanchu
11-15-2018, 06:57 PM
Yes, we call it a Derived DA - DDA (since we use it like a DA). We can use published MDA as a DA without the 50 ft buffer in a few specific cases. One being LOC approach with G/S OTS - as opposed to having no published ILS and just a LOC.

Another question - sorry, just being a geek tonight: It sounds like you're coming down in V/S or maybe FPA as you approach the derived MDA. Is that what you have in the ALT SEL? In other words, if you do nothing approaching that altitude, will the a/c level off at mins or continue down toward the runway?

I ask because when we used to do something similar in the MD-11, it would level at mins. The problem was, since you were already basically on glide path, if you let it start leveling off, unless you reacted almost immediately, it was going to be very difficult to get it back onto glide path. So, if you had to go right to mins to break out, you needed to disconnect the A/P no later than 200' prior to the DDA so you could stay on glidepath. Now on the 777 (and I think they changed on the MD too), you put runway elevation in the ALT SEL window so it keeps going down and you have to intervene to go missed (like an ILS) which makes much more sense since you're using a DA just like an ILS.


At the company I fly for (CRJs), we put the DDA(rounded to next higher 100') in the ALT SEL to get a descent started in VS. We then twist the missed approach altitude into the ALT SEL window after descending past the MAP alt. We get the minimums call at the DDA from what is set in the MDA, but the aircraft will not level off.

My original posting was concerning a different aircraft. The profiles that someone has established for it don't make sense to me.

One profile is along the lines of the dive and drive, but it has a derived MDA. The reasoning in this case is that the Autopilot might overshoot so they added the autopilot tolerance into the MDA and then round up.
That doesn't make sense because the purpose of having a derived altitude is to fly the non-precision like a precision with the added buffer.

The other profile is close to a continuous descent final approach, but then it doesn't have a derived MDA/DDA. Neither of the profiles that have been established seem appropriate.

Adlerdriver
11-15-2018, 07:17 PM
.... We then twist the missed approach altitude into the ALT SEL window after descending past the MAP alt.



One profile is along the lines of the dive and drive, but it has a derived MDA. The reasoning in this case is that the Autopilot might overshoot so they added the autopilot tolerance into the MDA and then round up.
That doesn't make sense because the purpose of having a derived altitude is to fly the non-precision like a precision with the added buffer.
We're coming down in VNAV the whole way, possibly from the IAF or even a feeder fix in order to hit all intermediate altitude restrictions on the approach. So, if we set MAP altitude and it's lower than the IAF or even FAF altitudes, it's going to capture on the way down the approach. Since we're VNAVing all the way down to the DDA (or DA on an RNP) we have to have something lower than all the altitudes on the approach including mins set in the FCP window (ALT SEL). So we can't set MAP altitude in the window until we actually make the decision to go missed.

You're right, that MDA plan doesn't really make sense considering you're never going to actually level off at mins. You hit the Derived MDA and you go missed. There's no point in buffering an altitude (due to A/P limits) that you're never going to actually level off at.

FlyPurdue
11-16-2018, 08:42 AM
I wish we did ‘CDFA’ on the 145s at Envoy. I repeatedly asked if dive and drive (while leveling out at each intermediate altitude no less) was really how we did LOC/VOR approaches, and was looked at like I had 2 heads when the instructor responded with a resounding ‘yes.’ So many opportunities to get slow/unstable.

To answer the question, we round up the MDA to the nearest 100 feet so we can put that in the altitude preselector.

galaxy flyer
11-16-2018, 12:21 PM
Does your planes have a VGP function for Baro/VNAV approaches, where upon path capture, VGP shows on the FMA, the ALT Selector becomes inactive and is set to missed approach altitude?

gf

FlyPurdue
11-16-2018, 12:28 PM
Does your planes have a VGP function for Baro/VNAV approaches, where upon path capture, VGP shows on the FMA, the ALT Selector becomes inactive and is set to missed approach altitude?

gf

Hi GF, I’m not sure whom that was directed to, but we did it at ExpressJet just like a poster above referenced at SkyWest; by adding XX feet to the MDA, and computing a V/S based off of GS. Here at Envoy it is a pure and simple Dive and Drive. Our RNAV approaches have a pseudo GP, but we only use it to LNAV minima.

galaxy flyer
11-16-2018, 01:00 PM
Well, probably aimed at either Adlerdriver or anyone flying airliners. The Collins in the either the Challenger or Global had VGP which armed with the approach loaded, APPR and VNAV selected. It would go VGP with Baro VNAV or LPV path captured, the ALT selector was then ignored by the system and these approaches were flown just like an ILS, with the requirement to add 50’ (DDA) to account for going below the MDA on the miss. There is an OpsSpec deleting the DDA requirement, IF the runway had been 1:34 surveyed.

I’ve been amazed or surprised at the differences between commercial and high-end bizjets avionics. Went into BDL, with the ILS down and flew LPV to land and several airlines weren’t capable.

GF

HIFLYR
11-16-2018, 02:01 PM
No, constant angle non precision approach. Add 50ft to the MDA. There are some approaches that require a dive and drive such as the LOC/DME 15 in Aspen.

We add 50' to the MDA of a V/S CDFA approach and call it a DDA derived descent altitude at FedEx. Some MDAs in VNAV require a DDA also, it is mainly driven by the TERPs assessment of the runway or aircraft specific limitations i.e. non compensated baro for cold weather or remote altimeter settings. We are FOM prohibited from doing a old fashioned dive and drive non-percision approach.
When I attended ARINC 424 meetings for my company and the group was working out the policies for VNAV approaches it amazed me all the differences of avionics and the companies attitudes. Some manufactures foresaw the treating of a MDA as DA in some cases and others said no way and went with PROF to MDA.

galaxy flyer
11-16-2018, 02:18 PM
See OpsSpec C073 for using the MDA as a DA.

OPSPEC/MSPEC/LOA C073, VERTICAL NAVIGATION (VNAV) INSTRUMENT APPROACH PROCEDURES (IAP) USING MINIMUM DESCENT ALTITUDE (MDA) AS A DECISION ALTITUDE (DA)/DECISION HEIGHT (DH).

GF

Adlerdriver
11-16-2018, 02:21 PM
Well, probably aimed at either Adlerdriver or anyone flying airliners. The Collins in the either the Challenger or Global had VGP which armed with the approach loaded, APPR and VNAV selected. It would go VGP with Baro VNAV or LPV path captured, the ALT selector was then ignored by the system and these approaches were flown just like an ILS, with the requirement to add 50’ (DDA) to account for going below the MDA on the miss. There is an OpsSpec deleting the DDA requirement, IF the runway had been 1:34 surveyed.
GF
The only mode on any transport category a/c (Boeing, AB, MD) I've flown that ignores the altitude in the ALT selector window is ILS, once the glide slope is captured. I think our VNAV needs to have a "bottom" altitude set in the window to calculate the vertical path accurately. When it stops needing that info exactly isn't something I know off the top of my head. We change it at 1000' AGL, so I know it doesn't need it from that point on down. The biggest thing is that unless we're on an ILS, the altitude in that window is never ignored. So, if MAP altitude was lower than the altitude we intercept the VNAV path on the CDA approach (and we set that), it would be captured on the way down.

We finally went back to selecting MAP alitude upon G/S capture on an ILS last month. Prior to that we were selecting runway elevation (like we would on a CDA non-precision) just to be standardized across all approaches. Then at 1000' AGL, we would select MAP altitude. It was pretty stupid considering probably 99% of our actual approaches are ILS and once I have the G/S captured, the next altitude I want in that window is MAP. Why would anyone come up with a procedure that gives us something to forget later in the approach just so we can do things exactly the same as we do on an approach we hardly actually fly. :rolleyes:

galaxy flyer
11-16-2018, 02:30 PM
That’s interesting, because the Collins system in Challengers and Globals use VGP which makes any VNAV approach just like an ILS with respect to the altitude selector. But, yes, in VNAV without VGP, you’d have to set the RWY or the path would end wherever to “bottom” was set in ALT SEL. The old Global had the Honeywell system and no VGP.

GF

EMAW
11-16-2018, 04:15 PM
Does your planes have a VGP function for Baro/VNAV approaches, where upon path capture, VGP shows on the FMA, the ALT Selector becomes inactive and is set to missed approach altitude?

gf

No the E145 wasn’t capable of coupling to an FMS glideslope, so no VGP.

HIFLYR
11-16-2018, 05:16 PM
The only mode on any transport category a/c (Boeing, AB, MD) I've flown that ignores the altitude in the ALT selector window is ILS, once the glide slope is captured. I think our VNAV needs to have a "bottom" altitude set in the window to calculate the vertical path accurately. When it stops needing that info exactly isn't something I know off the top of my head. We change it at 1000' AGL, so I know it doesn't need it from that point on down. The biggest thing is that unless we're on an ILS, the altitude in that window is never ignored. So, if MAP altitude was lower than the altitude we intercept the VNAV path on the CDA approach (and we set that), it would be captured on the way down.

We finally went back to selecting MAP alitude upon G/S capture on an ILS last month. Prior to that we were selecting runway elevation (like we would on a CDA non-precision) just to be standardized across all approaches. Then at 1000' AGL, we would select MAP altitude. It was pretty stupid considering probably 99% of our actual approaches are ILS and once I have the G/S captured, the next altitude I want in that window is MAP. Why would anyone come up with a procedure that gives us something to forget later in the approach just so we can do things exactly the same as we do on an approach we hardly actually fly. :rolleyes:

The VNAV path is encoded in the aircraft on board navigational database. It starts 50’ above the first brick of the runway and is targeted at 3.0 degrees. If 3.0 will not clear all step downs inside the FAF or final flight segment it will be raised.

Adlerdriver
11-16-2018, 06:25 PM
The VNAV path is encoded in the aircraft on board navigational database. It starts 50’ above the first brick of the runway and is targeted at 3.0 degrees. If 3.0 will not clear all step downs inside the FAF or final flight segment it will be raised.So, does it care what I have in the FCP window?

HIFLYR
11-16-2018, 09:24 PM
So, does it care what I have in the FCP window?

Depends on which avionics mfg. on the A300 it depends on if the appch is activated and in NAV OR LOC* and intercepted the VNAV path, once on the path in PDEC then no it does not look at FCP window as missed apch altitude is there. On the A300 bus with a grey box “honeywell” the minimum entry MDA/DDA just tells the autopilot when to disconnect.

cougar
11-16-2018, 10:20 PM
Some classification of approaches is necessary to address this topic thoroughly. OpSpec C052 now separates approaches into three categories; Non-Precision, APV, and Precision approaches. ICAO PBN is taking it a step further, where approaches are either an xLS, or a Non-xLS. An xLS approach is defined as an ILS, GLS, or MLS. The Non-xLS category is subdivided into either Non-Precision approaches or an Approach with Vertical guidance (APV).

All APV approaches are surveyed using a sloping Obstacle Clearance Surface (OCS) much like an xLS approach. This surface starts at the runway and continues to the FAF. For this reason, all APV approach minima are a Decision Altitude (DA), not an MDA, and the approach chart minima is labeled as a DA. As such, OpSpec C073 does not apply to APV approaches as it's redundant. APV approach types are LPV, RNAV(RNP) or RNP AR, and RNAV(GPS)/RNAV(GNSS)/RNP to LNAV/VNAV minima. Currently, no Boeing aircraft have LPV capability. Not sure if any Airbus aircraft are LPV capable, possibly the A350.

Non-Precision approaches are surveyed with a horizontal Required Obstacle Clearance (ROC) surface, such that no obstacle penetrates the ROC. The MDA must be 250' above the ROC, therefore the MDA is also a horizontal plane and cannot be penetrated by the aircraft unless the runway environment is in sight.

This is where OpSpec C073 applies. It allows operators to set a DA in lieu of an MDA for certain Non-Precision approaches that meet specific requirements. It is detailed, but in summary, if the Non-Precision approach is coincident with a VASI, APV or ILS approach, then the DA in lieu of a MDA may be used if the operator has the OpSpec.

If an operator doesn't have OpSpec C073, or choses to not apply it due to complexity, but still fly a Non-Precision approach using CDFA principles, then a Derived Decision Altitude (DDA) may be used. This is typically 50 feet added to the MDA, to ensure if a missed approach is executed, the MDA horizontal plane is not penetrated.

For Boeing aircraft with VNAV, the MCP altitude must remain below the aircraft to continue in a VNAV PTH descent, until the FMC is in "Approach Logic". Once the FMC is in "Approach Logic", the FCCs ignore the MCP altitude if it is more than 300' from the current aircraft altitude. Earlier FMCs (747-400 FMC) entered approach logic when the first fix of the approach was sequenced. Most modern FMCs on current production aircraft or retrofits like the NGFMC on the 747-400 enter approach logic when the flaps are out of up. Thus on approach using VNAV, the missed approach altitude can be set once the airplane is 300' below the missed approach altitude.

Finally, to help simplify Non-xLS procedures, all Boeing production aircraft are Integrated Approach Navigation (IAN) capable. IAN allows a Non-ILS to be flown exactly like an ILS. For example, for an RNAV(GPS) approach, the approach is selected in the FMC, and when cleared for the approach the crew simply selects the Approach switch. The FMAs will display FAC (final approach course) for the roll mode, and G/P (Glide path) for the pitch mode. Once FAC and G/P are active, the aircraft is coupled, and the missed approach altitude is set. The autopilot maybe left engaged until 100' RA typically. Just like an ILS, the only option to change pitch and roll mode is to select TOGA, or turn off the F/Ds and A/P. The downside is IAN cannot be used for RNAV(RNP) approaches due to RF Legs in the terminal segment, except possibly the 787.

Adlerdriver
11-17-2018, 06:21 AM
Finally, to help simplify Non-xLS procedures, all Boeing production aircraft are Integrated Approach Navigation (IAN) capable. IAN allows a Non-ILS to be flown exactly like an ILS. For example, for an RNAV(GPS) approach, the approach is selected in the FMC, and when cleared for the approach the crew simply selects the Approach switch. The FMAs will display FAC (final approach course) for the roll mode, and G/P (Glide path) for the pitch mode.
Thanks for the great info.

I'm confused by the bold above, since I've never seen either of those FMAs and IAN is not referenced in any of the Boeing manuals I've used. Would it be more accurate to say, "all Boeing production aircraft are IAN capable IF the operator buys that option"?

cougar
11-17-2018, 07:29 AM
Thanks for the great info.

I'm confused by the bold above, since I've never seen either of those FMAs and IAN is not referenced in any of the Boeing manuals I've used. Would it be more accurate to say, "all Boeing production aircraft are IAN capable IF the operator buys that option"?

Yes IAN is a customer selectable option. For the 747-8 it is an FMC OPC pin selection, which is no cost. However, other Boeing production aircraft may not include IAN as a standard configuration. Also, I forgot about the 767, which doesn't have an option for IAN capability to my knowledge.

FedEx 777s do not have IAN enabled?

pangolin
11-17-2018, 07:32 AM
If you are doing the traditional "Dive and Drive" method on a non-precision approach with the Autopilot Coupled, i.e. VS Mode, does any plane/company require an additive to the MDA due to the tolerances of the Autopilot capture/hold capabilities?

We don’t set the bottom altitude or MDA in the autopilot. In the last descent to MDA we set the missed altitude. At minimums we go around.

Adlerdriver
11-17-2018, 07:59 AM
FedEx 777s do not have IAN enabled?
No they don't.

Airbum
11-17-2018, 10:33 AM
We don’t set the bottom altitude or MDA in the autopilot. In the last descent to MDA we set the missed altitude. At minimums we go around.

Just a question, do pilots just have to remember the min alt?

We set the LNAV/VNAV minimum in the FCP altitude capture window on the MD11 at my airline. personally I like it that way. If you become distracted the FD/Autoflight levels the aircraft and will not fly itself into the ground.

Going above the projected decent path angle in my mind is much less a risk then a decent below minimums. Both require the pilots to make a mistake. One just has a much higher chance of killing you.

Adlerdriver
11-17-2018, 12:12 PM
We set the LNAV/VNAV minimum in the FCP altitude capture window on the MD11 at my airline. personally I like it that way. If you become distracted the FD/Autoflight levels the aircraft and will not fly itself into the ground.
:confused: So, do you worry about getting distracted on an ILS? On theses non-precisions, you set a DA or DDA in the baro mins and you have the same PFD indications of approaching mins and mins as an ILS.
You’re really worried about getting distracted on a non-precision approach and letting the aircraft “fly itself into the ground”? That’s a long time to be distracted. :eek:

Airbum
11-17-2018, 01:16 PM
:confused: So, do you worry about getting distracted on an ILS? On theses non-precisions, you set a DA or DDA in the baro mins and you have the same PFD indications of approaching mins and mins as an ILS.
You’re really worried about getting distracted on a non-precision approach and letting the aircraft “fly itself into the ground”? That’s a long time to be distracted. :eek:

I figured somebody would bring up the ILS, and you have a great point. In regards to being distracted for a long time someone posted above that the ROC for obstructions was 250' at MDA. With a VVI of close to 1000 a minute at max weight to me that's not a lot of time.

If able I don't want to give up the safety factor of a MDA backup. I know what I would choose, to set a DA/MDA. Perhaps I just am so used to it after decades of non ILS approaches I am reluctant to change. It seems most airlines do what you are talking about. Why did I waste all those brain cells figuring out a VDP!

The other point is a lethal accident we had where a crew impacted terrain short of the runway. If they had the autopilot on and a MDA set instead of a MAP perhaps things would have been different.

pangolin
11-17-2018, 01:30 PM
Both pilots set the mda. A blue line appears and the airplane says “minimums” when it occurs. If the two sides are set differently the airplane says minimums going through the higher of the two altitudes.

Just a question, do pilots just have to remember the min alt?

We set the LNAV/VNAV minimum in the FCP altitude capture window on the MD11 at my airline. personally I like it that way. If you become distracted the FD/Autoflight levels the aircraft and will not fly itself into the ground.

Going above the projected decent path angle in my mind is much less a risk then a decent below minimums. Both require the pilots to make a mistake. One just has a much higher chance of killing you.

Adlerdriver
11-18-2018, 10:20 AM
If able I don't want to give up the safety factor of a MDA backup. I know what I would choose, to set a DA/MDA. Perhaps I just am so used to it after decades of non ILS approaches I am reluctant to change. It seems most airlines do what you are talking about. Why did I waste all those brain cells figuring out a VDP!
For now, until the issues with the MD-11 923 FMS software get sorted out, you really don't have the option set anything other than MDA. The downside, IMO, to setting the MDA is you can't get to the actual DA/DDA while staying on the calculated glidepath with the autopilot on. As soon as the A/P begins the level off (~200' above mins, typically) you're going missed. Why compute a VDP? - so you can see, as you're starting to level off at MDA, yup - it's behind me now, so I have zero change of landing out of this. :D

So, if you want to fly right down to DA while remaining on path, you've got to disconnect the A/P no later than 200' above mins. If you decide to go missed at mins, now you get to hand fly the missed approach. Not a big deal but I think most guys would prefer the option to keep the automation on, especially with all those thrusties and a low MAP altitude, complex route or both.

Once MD-11 operators have the choice, I guess you have to balance the perceived benefit of the A/P leveling off at MDA on an approach you now probably can't land out of anyway with being able to automate down to mins and beyond whether you decide to land or miss.
The other point is a lethal accident we had where a crew impacted terrain short of the runway. If they had the autopilot on and a MDA set instead of a MAP perhaps things would have been different.
As far as the accident - MDA in the window might have helped. But, setting a descent floor and pre-programming mins is a procedural way to fly the approach and our clearance properly. To be blunt, it's not done to give us the leeway to so poorly execute an approach that the only reason we don't kill ourselves is because the A/P saves us.

cougar
11-18-2018, 11:02 AM
Why did I waste all those brain cells figuring out a VDP!

This is the epiphany I had about 20 years ago when I first started instructing on Boeing aircraft. The whole concept of a CDFA is that the airplane arrives at the MDA at the VDP simultaneously, therefore the VDP is rendered an atavistic term from the dive and drive days.

Further, since the DA/DDA is coincident with the VDP when using CDFA procedures, any level off at minimums likely leads to an unstable approach due to immediately being high relative to the intended glide path. This in my view is a far greater risk than forgetting and flying through minimums. As Adlerdriver pointed out, we seem to remember minimums just fine on ILS approaches. Moreover, the “approaching minimums” and “minimums” call outs are available as automated calls.

Training is the foundation for CDFA procedures, to ensure crews understand that once the descent has started at the FAF, there is no change, no ‘getting down early” etc. Maintain the briefed descent mode/rate, once at minimums (DA/DDA), continue if runway environment is in sight, or go-around.

For example, all Non-ILS approaches on the 747-400 can be flown in VNAV, therefore VNAV PTH is the required FMA from the FAF until the End of Descent point per our company procedures. If the FMA changes from VNAV PTH to any other mode inside the FAF, it requires a go-around.

If V/S is required to fly the approach (this would only be necessary due to some NOn-normal), then once the calculated V/S descent rate is set at the FAF, is doesn’t change. At DDA, continue or go-around.

PerfInit
11-18-2018, 01:27 PM
Another thing to consider - Is the 34:1 “clear” from MDA (DA/DDA/VDP) to 50ft above the landing threshold? A few years ago, FAA TPP added a light grey “stipple” symbol on the profile view of the plate. This indicates that the imaginary 34:1 surface is clear of penetrating obstructions. Flight Check verifies this during their periodic inspections.

Absence of this light grey “stipple” symbol on FAA plates means “look out below” and make sure you visually follow the PAPI or VASI (stay on the PAPI/VASI glidepath). Hence the reason that many chart notes specify “VGSI Not Coincident”. Translation: Remaining “on path” using VNAV guidance only might be hazardous during some non-precision procedures.

Also please note for awareness that Jeppesen Does Not Currently Publish this same “stipple” symbol/feature on their products. For more info, see the AIM and related AVWEB article on this a few years ago. If I can dig up the link I will post it here:

https://www.avweb.com/news/features/Danger-Below-MDA-223713-1.html