Descent When Cleared For Approach

[W.SHIRRA]

A question for those who know everything:

You are established on LOC after a radar vector, maintaining 4000ft.

The published procedure shows the whole approach at an altitude of 2500 ft, and a glide intercept at that altitude.

The controller than says you are cleared for the approach: are we obliged to capture the glide at 4000ft, or can we take the initiative to descend at 2500ft, then capture the glideslope?

All minima are satisfied in my scenario (MSA, Radar Minima, Approach Plate Minima etc...): I'm asking about the initiative to descend to a lower altitude when cleared for the approach.

Thank you for your help.

[Phil Squares]

Once you are established on a published segment of the approach and cleared for the approach, you may descend to the published altitude for that segment of the approach.

In this case, you would be "legal" to descent to 2500' and intercept the G/S at that altitude. Personally, I would just maintain 4000' and intercept the G/S at that altitude. But that's just my preference.

[604guy]

Operating under the assumption that there are no intervening factors i.e. mandatory crossing altitudes etc then my question would be...why would you want to start a descent to 2500ft? Given your scenario I am assuming that you are established on the LOC and you are currently below the glideslope. I think it better practice to maintain 4000, intercept the GS and then down you go in one continuous stabilized descent to the runway. I am not sure why you would want to descend to 2500…intercept the GS and then start your descent again. However the answer to your query is that given the scenario described then yes you technically could start your descent to 2500 providing as you say that you meet any and all restrictions detailed on the plate.

[Rainboe]

I think the reason is that glideslopes are only guaranteed to 10 miles out, therefore technically 4000' aal is going to be outside the coverage area for the glideslope and so you should strictly descend to 2500' then continue descent. This is why many approaches show stepped descents until within 10 miles. The glideslope is accurately aligned as a final approach aid, not an intermediate approach facility.

[Rubberjungle2]

I was under the impression the promulgated range of a useable Glideslope signal was 15nm and a localiser was 25nm...?

[rigpiggy]

our autopilots sometimes take a while to get sorted out. given the choice stay at 4000 till the slope and give the piece o crap lots of time to figure itself out

[Shore Guy]

It is my understanding that if on a published segment of the approach, one can go to the altitude depicted for that segment. But at the FAF, one must verify altitude to confirm on the proper glide path.

The ultimate “Cleared for the approach” accident….one that sparked many changes and the development and implementation of GPWS.


http://www.aopa.org/asf/asfarticles/sp9806.html

[W.SHIRRA]

Thank you so much for all the replies.

I preferred to descend to a lower altitude to keep high speed.

The lower the altitude at which you intercept the glide, the faster you can fly until then. Instead of extending flaps to 5 (737) and descending at 180 knots from 12 NM out, I kept 280 knots until level at 2500ft, then slowed down. Worked nice.

:ok:

[mondriver]

Word of warning though perhaps...

Exceeding 250kts at that sort of altitude puts you in GPWS terrain closure rate territory and you may find yourself having to perform a rather unwanted GPWS recovery.

Personally, I would intercept at 4000; be stabilised and more importantly...safe.

;)

[normal_nigel]

If LHR cleared you to 4000 and then told you to descend with the ILS I would imagine they would go mad if you dived down to 2500 and then did it?

It could be they have helicopter traffic over London and seperation couldbe compromised by doing so?

Perhaps Heathrow Director can advise?

[HEATHROW DIRECTOR]

OK.. but remember I'm retired and don't want to tread on any toes..

This is precisely why we have the strange phraseology in the UK, to prevent anything untoward occurring. If, as a controller anywhere in the world, I cleared someone for an ILS (or other type of approach) I would expect the pilot to do what he deemed necessary to complete the approach in accordance with HIS procedures. I.e in the scenario referred to I would expect ATC to ensure separation in anticipation of the pilot descending to 2500ft. (Let's not get involved too much in the range of ILS installations).

At Heathrow, for the reason normal_nigel notes (among others), you won't be "cleared for the ILS" so the situation should not arise.

[duckbelly]

OK, How about this one:

I've spent most of my flying career in OZ, the last two in the UK.
One phrase that always had me foxed was the
'Descend to XXX', further with the glide.'

On the face of it I suppose it means intercept the glideslope and keep on going. I couldn't find anywhere the phraseology so wouldn't descend until we were 'Cleared for the approach', much to the consternation of some of the FO's.

Who was right?

[alexban]

shirra: 280 kts at 2500'?...at what distance to rwy?
Boeing FCTM says that you should have 210 kts at 12 dme,and also that it will take a total of 6 NM to reduce speed from 280 kts to 210 kts in normal conditions (no wind ,normal weights..)
so,I guess you'll have 280 kts at around 15 NM,then start reducing to be with 210 kts at GS intercept.
A bit tight,especially if you happen to encounter a tail wind on this segment.
I see you fly in Africa,so I guess you can do all this there ,just for fun.
But in a crowded airport you'll have to do your speeds right,maintain separation,speed restrictions,etc...
Also ,if you want to play it safe you should do the preparations for landing sooner,as not to be rushed by anything ,and to be fully stabilized on app,above 1000'.
In this particular case I would go for GS at 4000',stabilized,etc...
One question ,though. How much time do you think you're gaining by doing the app the way you said ( keeping 280 kts at 2500' ) ? I bet less then 30 sec.
And also,what do you think of a bird strike at that speed,compared to a strike at 100Kts less (180 at flaps 5 on GS ,from 4000')?
Fly safe,and you'll have a lot of fun.
Brgds Alex

[Miserlou]

Shirra,
Do please work out and inform us of this time saving you think you're getting. Do remember to take TAS into account and, while you're at it, do a fuel calculation too.

Maintaining 4000´and going with the glide would be my advice any time but for wake turbulence reasons in addition to those mentioned above.

[W.SHIRRA]

ALEXBAN
that took place in Roma, for rwy 34R.
Instead of flying north to CMP , since I anticipated the controller to be smart, I descended much earlier, and was cleared to cut all corners of a very long S pattern, saving at least 30 miles.

And that's what happened: the controller suddenly cleared me direct to the loc, for an almost straight in ILS.

I agree 30 seconds is not much, but when you are late and blessed with such a short cut by ATC, you enjoy it!

Being stabilized at Vref above 1000 ft is paramount to me, and I was.

Birdstrike? So you never fly without speed restriction below 10000ft?
If it happens, it happens.
Sorry for the bird! :p

Btw: when I say north of Africa, I mean the southern peninsula of Eurabia: Italy!

[ManaAdaSystem]

What about; You're cleared approach, maintain 4000 ft? Has happened to me more than once, and I still don't have a clue what they mean.

[FlexibleResponse]

I bags to fly with 604guy as my crewmember!

A very eloquent answer, compete with professional knowledge and spiced with that sometimes rare but essential ingredient for pilot longevity, commonsense.

[JustaFew]

In the UK, the term is usually used to allow an aircraft to carry out a procedural instrument approach WITHOUT leaving or descending below a stated level in order to avoid meeting another plane below it. Looking at the approach plate, carry out the PLAN track but NOT the side elevation part until ATC gives you descent clearance.

[alexban]

Shirra:
aa,the well known FCO atc. In this case ,I bet you were already in a tight situation,as I know very well their proficiency.
It's a lot of fun going there,every time.Especially when you're cleared for a rwy,by 3-4 atc sectors,then kept high and fast,and in the last second ,cleared to turn and intercept the ...other rwy.
As I said,a lot of fun....
The 604guy answered well to your question.
And ,regarding birds strike ,I wouldn't be so careless.Recently,we had to replace an entire fan (737Cl) due to birds strike ,and it was at low speed ,just after take off.
There are some interesting photos on the net ,regarding birds strike,just do a search.The faster you go,the bigger the hole,I think.
Alex