3 interesting interview questions...

[j328ernest]

Received some interesting practice interview questions recently:

1. A contaminated runways affects which speeds? I think it's V1, Vr, and V2. Am I correct and complete? (Someone else said Vy but I can't figure why.)

2. When does an instrument approach turn into an 'Alpha' approach? I thought it was when the final approach SEGMENT course versus the applicable runway centerline headline differed more than 30 degrees from each each other, thus requiring it to be a circling approach. Am I correct?

3. Under IFR rules what are the lowest takeoff WX mins under Part 91? I though unless the departure point had an IAP with either applicable takeoff WX mins or published straight-in landing WX mins there are none - in other words either none OR (on a guess, entering Class G airspace it would be 1 mile) Am I correct?

Thanks in advance to the professional respondants...

 

[Dave Benjamin]

1. As far as effecting speeds the only one I can think of is V1 because of braking considerations. After V1 you're committed regardless of what Vr happens to be. Uually they are the same or very close. V2 only applies when airborne and is your single engine climb speed in the second segment. For landing purposes Pt 121 requires you to have 115% of the normal runway length available if the runway is contaminated (turbojets only). The runway length requirement is predicated on the AFM numbers plus a 70% buffer for destinations or a 60% buffer for alternates.

2. Read the intro section of the Jepps or look in your AIM. You might also want to know something about SDF and LDA approaches in case you have an interviewer that likes to talk about that stuff.

3. PT 91 IFR T/O mins are 0/0. Whether that would be prudent is debatable. I don't know about other operators but we have our own restrictions on Pt 91 takeoffs that supersede the FAR's. We are rarely Pt 91 except for a test flight or reposition.

I see we both have some time in the mighty Luscombe. Feel free to PM me.

 

[COEX_av8r]

2. When does an instrument approach turn into an 'Alpha' approach? I thought it was when the final approach SEGMENT course versus the applicable runway centerline headline differed more than 30 degrees from each each other, thus requiring it to be a circling approach. Am I correct?

Also, you can have a final approach course lined up with the runway and still be an "Alpha" approach. Because of terrain, the approach may not allow a "normal descent to landing" from the MDA, thus requiring a circle. Can't think of any good examples off the top of my head to point you towards.

 

[Gulfstream 200]

I have seen V1 and VR both move on contaminated runways.

On some aircraft where V1=VR normally, I have seen them split them by 10 or so knots - add 5 to one and take 5 off the other....for contamination.

another interesting concept is the definition of contamination itself.....can be downright scientific by some accounts.

 

[Rogue5]

Re: Re: 3 interesting interview questions...

Also, you can have a final approach course lined up with the runway and still be an "Alpha" approach. Because of terrain, the approach may not allow a "normal descent to landing" from the MDA, thus requiring a circle. Can't think of any good examples off the top of my head to point you towards.

If you've got a copy of the CA Jepp plates, look at Hayward, CA (just south of Oakland). They've got an "- A" approach that almost directly aligned with the runway, but because of the excessive altitude loss only circling mins are published, though this, as they say, "does not preclude a straight in approach and landing."

 

[Snoopy58]

1. GENERALLY, only V1 would change. Three caveats to that: if the runway is long enough, it could remain unchanged (i.e. = to VR). Also, on SOME aircraft with unique performance data, anything is possible -- i.e. what is mentioned above. Also, if OTHER things change because of the contamination (i.e. it drives you to a max power takeoff instead of reduced thrust, for one example), then the V-speeds may change as a result of THOSE changes, rather than the contamination itself. That's aircraft & operation-specific, though. In the most general case, there's no reason to rotate at a different speed on a contaminated runway.

2. An instrument approach becomes a "-A" approach when it is a circling approach. Period.
The next question might be, what makes an approach into a circling approach, and my recollection is that it can be any of 3 things: final approach course not aligned within XX degrees of any runway, OR MDA "too high" for a normal landing, defined by some criteria that I can't quote off the top of my head, and a mystery third factor that's escaping me at the moment. Sorry about that.
An example of the "MDA too high" would be an approach with very high terrain in the area, such that the only way to make the missed approach procedure "work" (in terms of climb gradients) is to make the MDA very high above the runway. Then, the only way to get from the MDA to the runway would be to do something of a circling nature (say, a couple of honking S-turns, putting yourself roughly on a VFR base leg to the runway). So they designate the approach as a circling approach, even if the final approach guidance is straight down the runway.

However, all of the above factors are for approach DESIGNERS. What a pilot needs to know is, if it's a "VOR-A," it's a circling approach.

3. I think zero-zero is correct for part 91 by virtue of nothing else published, as explained before.

 

[Stifler's Mom]

If I remember correctly, Key West, FL (EYW) has an Alpha approach for an alignment less then 30 degrees off, due to excessive decent necessary to get down.

 

[probablecause]

Interview Question

I’ll play. We have all heard of mountainous and non-mountainous terrain right? So how do you determine which is where? Is it published somewhere?

PC

 

[KPTO]

interesting interview questions

Since V1 is really an accelarate/stop distance calculation
and the runway braking action is affected by contamination
one would have to have a slower speed in order to be able to reject
the take-off safely.

Aside from 30degrees, descent rate and obstructions the TERPS specialist can use time to miss as a limiting factor. There is an a pproach in west Texas in which an ac at 70knots would have less than 45 sec between the Faf (an off field ndb ) and the MAP. This is related to what has been mentioned before as
excessive descent rate.

No PART 91 has no Take-off Min. Been there done that with a low and local fog bank it was 100/1mile. Did not care for it.

Ernest I think we met at MKE a few weeks ago. PM if you have time and let me know what is going on.

 

[DaveyDave]

Re: Re: 3 interesting interview questions...

Also, you can have a final approach course lined up with the runway and still be an "Alpha" approach. Because of terrain, the approach may not allow a "normal descent to landing" from the MDA, thus requiring a circle. Can't think of any good examples off the top of my head to point you towards.

I think Roanoke has an approach like that, a VOR approach to the south. You are dead aligned with the runway, but come through literally a gap in the mountains on the final approach course, and the MDA is way too high to land straight in with anything other than a 172. Neat approach.

 

[reject007]

Mountainous Terrain? The Jepp has a chart (map of the USA) in the Intro section that will show you what is considered mountainous terrain. I also remember a definition of mountainous terrain, which you can find in the definitions section of the Jepp. Try looking under one of the Minimum IFR altitudes...and I believe it says that mountainous terrain is any terrain where the elevation exceeds 5000' MSL.

I'm doing this off the top of my head, so I apologize if there are discrepancies.

 

[upndsky]

The AIM has a map of the US that shows areas of mountainous terain with shaded areas. Unfortunately, the map's the size of a postage stamp so good luck trying to figure out where the boundaries are. But if I recall, it basically is the Appalachians from GA up through the Northeast and almost anything beginning east of the Rockies westbound.

 

[Stifler's Mom]

Here's another question, why on some Jepp plates are the surrounding elevations "brown"? I've noticed that it is usually terrain that is 2000' above airport elevation. Any answers????

 

[GeorgeTG]

ok i'll bite

--"Alpha" approach aligned (<30 degrees) with runway means descent gradient is in excess of 400 ft/NM.

--- Terrain or obstacles will raise MDA or DA(H)

-- Terrain contours depicted when:
Highest point on plan view exceeds 4000ft AFE or terrain rises above 2000ft AFE within 6NM (I dont have my Jepps handy, but I belive this is correct. In any case the Jepps into pages will spell it out...)

 

[Hawker rider]

mountainous terrain is defined as terrain being higher than 5000' msl.

strange that there don't have to be mountains in the area for it to be considered mountainnous.

For the same reason I was always taught that in mountainous terrain the MSA ( for instance) always included 2000" obstacle clearance, opposed to non-mountainous terrain having 1000' abstacle clearance. I swear somwhere the other day I noticed an obstacle being above 5000' and only having 1000' obstacle clearance

 

[reject007]

MSA's only provide 1000' obstacle clearance in both mountainous and non-mountainous terrain. I believe that's the only exception to the rule.

 

[wmudriver]

Weird Questions

Here is a few I heard floating around...
Have you ever seen a grown man naked? Have you ever spent time in a Turkish prison? Have you....I'll stop

 

[pitot-grande]

The use of an alphabetical suffix indicates a procedure does not meet criteria for straight-in landing minimums. The VOR-A at KSDM and LOC-D at KSEE are two examples that come to mind.

 

[ClearRight]

Here's another question, why on some Jepp plates are the surrounding elevations "brown"? I've noticed that it is usually terrain that is 2000' above airport elevation. Any answers????

I've got a few plates with some of that brown terrain-looking shading. OMA is one. . . could be from that coffee I spilled a while back!

 

[100LL... Again!]

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strange that there don't have to be mountains in the area for it to be considered mountainnous
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Typically, altitudes on approaches are not adjusted unless the surounding terrain is considered 'precipitous'. The altitude buffer is to allow for localized pressure changes due to wind flowing over terrain.

In the very north lattitudes, cold weather corrections are often made to altitudes on the approach to compensate for the contraction of the pressure levels.


In answer to the above questions,

#1
In theory, only V1 should change. However, if you read part 25, you will see that Vr can depend on V1. You will also see that V2 can depend on Vr in some cases.

So I would say that V1 is directly affected, while Vr and V2 COULD be indirectly affected. Not likely, in my personal opinion.

#2
Well explained by above posts.

And it is true that the max descent gradient from the faf to a point 50 ft above the landing threshold can not exceed 400 ft per nm.

Interestingly, MDA is not considered in this calculation.

Therefore a dawdling descent to MDA could leave you unable to descend normally to the runway. Dive and drive, baby!! (Anticipating flames over this).

#3
Zero-zero is correct