Instrument approach question

[Jetheat]

If you are localizer established 12NM out and the controller clears you to descend to 2000 feet - The MSA on Jepp and Aerad in that sector is 3900 feet but the spot height on Aerads at that particular point (12 NM out)is 1800 feet. Would u descend?

[FlapsOne]

Visual, Under Radar, on or above Glideslope - Yes

[Jetheat]

The glideslope would not have been intercepted at that point. Does that mean that the spot height on the Aerad actually means MSA? Does that mean that u can descend to that altitude of 1800 feet?

[COWPAT]

At 12nm and looking at MSAs, the figure quoted on (Jepp) charts will be the MSA out to 25nm. Therefore, if you are under positive radar control, you would be safe down to 2000 ft. This, of course, does not absolve the aircraft commander of his responsibilities towards the safe conduct of the flight.

The benefits for ATC and the operator of doing this are that it enables an intermediate app speed (210 kts ish) to be maintained for a longer period and results in more movements/hr for atc and less fuel burn for the operator.

If in any doubt though, wait for the G/S.

[quid]

Sure, descend to the cleared altitude. If you're in radar contact, the controller can (and will in many cases) clear you to the MVA (minimum vectoring altitude). MSA is the worst case altitude.

To take it a step further, if you are cleared to an altitude, you are expected to comply "in a timely manner". You can't ignore the clearance unless he says "Pilot's discretion".

P.S. Just because you are showing glideslope indications is no guarantee that the information is usable or accurate. Normal glidslope service volume is 10 NM, but many are flight test further out. You don't know unless it's published.

Warnings about following glideslopes at distances further out than published are repeated every few years in the ALPA magazine.

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[This message has been edited by quid (edited 13 November 2000).]

[GMS]

Jetheat,

You talk of a "spot height" of 1800 ft.

Do you actually mean a contour elevation of 1800 ft? If this is the case, your terrain clearence at 2000 ft. will be at least 1200 ft. at your present position, and 1700 ft. above the airport.

[Jetheat]

Spot height - I believe on Aerads this may well be the MSA in that area.

[Check 6]

The MSA on Jepp charts is an "emergency altitude" only, not to be used for routine navigation. The MSA will only provide 1000 feet obstacle clearance within the depicted circle. Using the MSA otherwise has potential for disaster.

Cheers,

Check 6

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Kick the tires, light the fires, first off is lead, brief on guard.

[GMS]

Jetheat,

I should not have said "contour elevation", I should have used the Aerad term "MSA Contour Envelope".

It does make a difference to what charts you are using. I use Aerad, but have used Jepps in the past and if I remember correctly they do show spot elevations ( not heights ) with an arrow.

Terrain clearance with Aerads is as I mentioned on my previous post.


[This message has been edited by GMS (edited 15 November 2000).]

[EmDeer]

Not an answer to the original question, but it´s topic related...and please excuse my bad english ;)
(excerpt of a summary of the IFALPA conference in Tokyo, 7. – 11. April 2000)

PROVISION OF MINIMUM VECTOR ALTITUDE CHARTS -

This Policy is currently subject of a working group under the lead of Frank Mueller-Nalbach (VC). It will be recommended that on airfields on which radar-vectored descents below MSA are common, flight crews will be provided with so-called "Minimum Radar Vector Altitude (MRVA) Charts". This way situation awareness can be enhanced by continous crosschecking your position.
Since it is the "worst case" of obstacles in the periphery of 20 NM around a navigation fix, radar controllers may disregard the MSA due to their exact knowledge of the location of any obstacles and the position of the approaching aircraft. However, it is important (e.g. in the event of a communication failure) that the flight crew knows the minimum altitudes in their approach path, so the MRVA charts are considered a necessity.
The working group will work on the policy to have it ready (including a proposed presentation of the MRVA charts) for the next IFALPA conference in the year 2001.

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You can´t make it foolproof.
Fools are too inventive.

[Ignition Override]

EmDeer: Ihr englisch sieht ganz gut aus. Viel besser als mein d.

As for 2,000', you should be OK: After the TWA tragedy in the mountains of Virginia many years ago (not too far from Dulles Int'l/IAD), airlines usually remind pilots to remain at the:

"last assigned altitude until established on a segment of a published instrument approach".

Believe it's either a US FAR or in the Airman's Info. Manual?

[This message has been edited by Ignition Override (edited 21 November 2000).]

[This message has been edited by Ignition Override (edited 21 November 2000).]