Vertical path non-precision approach safety?

[Zephyr]

@Zephyr. Excellent read. Other than crawling the TERPS, do you know of a document that discusses G/P and VGSI not coincident obstacle clearance?

Thanks

There isn't a handy reference that addresses this explicitly, but it can be inferred. No protection between a non-precision MDA and the runway is discussed in the 8260.3B, however it discusses the GQS, which provides protection for approaches with a DA.

The 6850.2B addresses VGSI standards, which includes obstacle protection out to 4 miles (slight differences between VASI and PAPI, but they are mostly similar).

The requirements to apply a derived DA listed in Opspec C073 also provide insight into ways a non-precision approach can effectively be protected between MDA and the runway even if the approach itself doesn't offer protection.

 

[Polar742]

There isn't a handy reference that addresses this explicitly, but it can be inferred. No protection between a non-precision MDA and the runway is discussed in the 8260.3B, however it discusses the GQS, which provides protection for approaches with a DA.

The 6850.2B addresses VGSI standards, which includes obstacle protection out to 4 miles (slight differences between VASI and PAPI, but they are mostly similar).

The requirements to apply a derived DA listed in Opspec C073 also provide insight into ways a non-precision approach can effectively be protected between MDA and the runway even if the approach itself doesn't offer protection.

Thanks for those references. C073, while we have it, doesn't have reasoning beyond the rule itself.

Thanks again.

 

[Zephyr]

Thanks for those references. C073, while we have it, doesn't have reasoning beyond the rule itself.

Thanks again.

Sure. The requirements listed in C073 all feature 'hard' obstacle clearance surfaces, which must be clear. For instance, the requirement for the runway to be served by an ILS, LPV, LNAV/VNAV, etc. approach has a hard obstacle clearance surface through the GQS. The requirement to have a VGSI has its own hard obstacle clearance surface. If the VGSI is at a higher angle than the approach glidepath, the approach isn't eligible because following the glidepath would put you below the obstacle clearance provided by the VGSI. The non-precision approach that will offer the DDA essentially piggybacks on those hard surfaces. I think the requirements in C073 are surprisingly pragmatic for something put out by the FAA...

 

[MoMatt]

This thread has been thought-provoking and I'd like to define / clarify some things as I understand them so those "under-informed"(like myself) may benefit.

CANPA - constant angle non-precision approach. Is this standard in 121? Is it a required technique, or do you have the option to "dive and drive"? Sounds the same / similar to CDFA, but I can't find reference to it in my 135 material.

CDFA - continuous descent final approach. Referenced at the end of C073 (which is here) states that the operator may choose to use a continuous descent rate (instead of "dive and drive"), but MUST begin a missed approach above the published MDA so as not to descend below the MDA during the missed.

Our ops spec C073 reads as giving us a choice to fly the approach as a "dive and drive" or as using MDA as a DA/DH.

OPS SPEC C073 - Basically says that if you have a non-precision approach to fly, you may fly it using the MDA as a DA/DH as long as a bunch of requirements are met, specifically:
- The approach you want to fly is to a runway that also has a precision approach (ILS, MLS, LDA, or RNAV/GPS with published LNAV/VNAV DA), or to a runway with a VASI / PAPI

AND

your desired non-precision approach has a flight-path angle (GS or vertical descent angle) the same or greater than the precision approach or VASI / PAPI to the same runway.

As explained by @Zephyr, this is a TERPS protection so you have a protected glidepath to the runway.

If these requirements aren't met, C073 says you can still use a CDFA, but must execute the missed so as not to go below the MDA, since that chunk of airspace does not meet TERPS requirements for a precision approach.

Back to the OP - it looks to me like if you're going to fly a CDFA / CANPA / DA in lieu of MDA, you better make sure the runway you're going to has been TERPS-stamped for a precision approach, or you better go missed without going below MDA. Otherwise you aren't protected.

 

[Boris Badenov]

Between misunderstanding of this topic among pilots and the opportunity for confusion between real and derived glidepaths as depicted on avionics, I think this will lead to an accident someday.

Wait, no one called you a jerk.

 

[mikecweb]

Wait, no one called you a jerk.

Because he has the skills to pay the bills.

Annnnnd he's a former starchecker.

 

[derg]

Wait, no one called you a jerk.

Here's a hug.

There, there...

Ok. Back to the discussion!

 

[BobDDuck]

My biggest point of advice on Douglas equipment like the DC-9 series, of course I've never flown the 717, but if it's anything like the rest of the DC-9 variants, consider the auto throttles as "Santa's Little Helper", but you are Santa.

Follow them though with your hand, watch them like a hawk and if they're not moving when they should, move them where they need to be.

One of my biggest problems when I transitioned to the "80's Modern" 75/76 was keeping my hands off the throttle during climbs, descents and the early parts of the approach phase.

The good news is that it seems like most guys turn them (and the autopilot) off at TOD or 35 miles out when we can call the field for a visual.

 

[BobDDuck]

Wait, no one called you a jerk.

Your argument is Irrelephant.

 

[Autothrust Blue]

Non-precision approaches can effectively be protected between the MDA and the runway if there is a VGSI (with an angle equal to or less than the approach glidepath angle) or another set of minimums having a DA and the same glidepath angle for that runway. This is the spec that determines whether a derived DA is approved for that runway or not.

On a non-precision approach, if the VGSI is at a higher angle than the approach, the VGSI is protected, but the glidepath is not.

Visual areas are evaluated during procedure development, but are not required to be clear. Penetrations only result in increased visibility minimums or restrictions on the procedure. It should be noted that if the 20:1 visual area is penetrated by unlit obstacles (meaning, something is higher than you are within the visual area), the procedure will be NA at night, HOWEVER a VGSI may be used in lieu of obstruction lighting. This means that if the VGSI is at a higher angle than the approach glidepath and you wind up low on the VGSI, you're not protected.

Eeeeep. That's REALLY good to know, thank you.

Although, of course, you're required to remain "at or above" the VGSI for a runway until a lower altitude is "necessary for a safe landing..."

 

[Zephyr]

Wait, no one called you a jerk.

Hah. What got me going on this topic originally was when I sat in a room with reps from a bunch of major airlines, and they all said that it was their SOP to stay on the derived glidepath on non-precision approaches (citing CDFA/CANPA). *facepalm*

 

[Zephyr]

Eeeeep. That's REALLY good to know, thank you.

Although, of course, you're required to remain "at or above" the VGSI for a runway until a lower altitude is "necessary for a safe landing..."

Then look both ways before descending

 

[Autothrust Blue]

Then look both ways before descending

Unless you're flying freight to a jet, have a cargo of radioactive rat semen, or something like that.

 

[Autothrust Blue]

Hah. What got me going on this topic originally was when I sat in a room with reps from a bunch of major airlines, and they all said that it was their SOP to stay on the derived glidepath on non-precision approaches (citing CDFA/CANPA). *facepalm*

Applying this to an approach like the LOC 27 to San Diego (Lindbergh), my Jepp says "VGSI and descent angles not coincident." This seems to imply that upon arrival at (D)MDA, a change in flight path angle is required to intercept the VGSI and therefore not hit the parking garage. Is this correct?

 

[derg]

Your argument is Irrelephant.

Hot damn, you beat @Minuteman to it! Good work, sir!

 

[PeanuckleCRJ]

I'd pretty much decided to let this one sit, since I've never flown anything over 16.3 gross weight, and maybe it's true that the increased inertia of all that weight makes levelling off at the step-downs like sticking your head in a lion's mouth (although one does wonder a bit how all those drunk guys in awesome hats did it in 707s day in and out without crashing). But as a blanket claim for all aircraft, the notion that having to, you know, FLY AN APPROACH makes things more Dangerous is utterly absurd. I know we all like to think of ourselves as Rocket Surgeons, but flying a non-precision approach to minimums is about as difficult as merging on to an expressway, provided you have the proper skillset and appropriate training. This is not curing cancer, FFS. Read the plate. Fly the plate. If the statistics indicate that we're crashing on a lot of non-precision approaches, maybe the problem isn't with the approaches, but with the fact that "we" are eating too many paint chips as children.

Great googly moogly... are you being purposely obtuse?

The advent of the constant descent angle non-precision approach technique (and further refined with vnav overlay) came about because so many of the drunk guys in awesome hats in old jets were hitting things and killing lots of people with considerable routine.

 

[Zephyr]

Applying this to an approach like the LOC 27 to San Diego (Lindbergh), my Jepp says "VGSI and descent angles not coincident." This seems to imply that upon arrival at (D)MDA, a change in flight path angle is required to intercept the VGSI and therefore not hit the parking garage. Is this correct?

It looks like that approach isn't eligible for a DDA, so you're correct. To guarantee that you won't hit the baby on the parking garage, you would ride the descent angle down from the FAF to the MDA, level off momentarily until you intercept the VGSI and then ride that down. Of course, a parking garage is fairly well lit Hills and trees, not so much.

 

[derg]

Looks like we'd fly it to "ball note #2" and then pick up the visual.

At my employer, on my specific equipment (which means yours may differ in a variety of ways), that when we use the VPATH deviation, we're almost monitoring "Progress Page 2" for a numeric value of any VPATH deviation.

According to our procedure, if you're heads down after DA following either when you should be flying visual, you're making a potentially hazardous mistake -- because if the PM is heads-out monitoring your VPATH deviation that low, he's out of the loop and the PF is being a test pilot doing this own thing.

Edit for addition: Plus, if you're that low, that's going to kick your ass isn't as much the VPATH indication, it's your FMS going into VSPD mode where it's maintaining airspeed and not VPATH. You're too low to be dicking around with the magic at that point and if you're doing it, STOP. It's not an ILS.

 

[PeanuckleCRJ]

My biggest point of advice on Douglas equipment like the DC-9 series, of course I've never flown the 717, but if it's anything like the rest of the DC-9 variants, consider the auto throttles as "Santa's Little Helper", but you are Santa.

Follow them though with your hand, watch them like a hawk and if they're not moving when they should, move them where they need to be.

One of my biggest problems when I transitioned to the "80's Modern" 75/76 was keeping my hands off the throttle during climbs, descents and the early parts of the approach phase.

Bingo. Don't forget that THR HOLD is the same as IDLE CLMP and can bite you just the same. I'm willing to bet that is what bit the Asiana guys in SFO. I rode the throttles pretty good in the Boeings, too when I realized the same weak link existed.

Similarly, watch yourself in THR IDLE on fifi.

 

[derg]

Bingo. Don't forget that THR HOLD is the same as IDLE CLMP and can bite you just the same. I'm willing to bet that is what bit the Asiana guys in SFO. I rode the throttles pretty good in the Boeings, too when I realized the same weak link existed.

Similarly, watch yourself in THR IDLE on fifi.

I thought of "THR HOLD" as "We're not going to move any more in this vertical mode" and "CLMP as XX-Manual Positioning"

Keep an eyeball on that TARP panel because, after all, whether you're flying the steampunk DC-9-15 or a 717, it's an after-market mod'd DC-9.