precision approach with AIRPORT data only?

[wanabe2010]

is it possible to approach with the airport databank only.

I explain, a pilot is on an approach with minimum fuel where a go around is not possible(Mayday situation). Suddenly the only instrument approach is inop and you have to land the plane.

ceiling is around 100ft agl.Can be 50 ft...

Can you just draw a line from the runway, and follow this line?.

how far will you be away from the centerline?
is this kind of approach recommended in this type of situation?

[welliewanger]

Hi,
I'm not sure what you mean by "airport databank".

Not enough fuel for a go around is very unlikely because of the legal requirements for minimum takeoff fuel. You'd have to be having a particularly bad day not to have enough to go around.

The weather picture you've painted is also unlikely and would prompt any captain to take even more fuel. Many aircraft couldn't land in those conditions even with everything working.

So, if your question is "If there were no approach aids, how close would the on board navigation systems (with or withouth GPS) get you to the runway?" then the answer is... pretty close! IRS (if you've got it) is fairly reliable, if you've got 3 of them and they average the position, you might not hit the runway, but you would probably hit the grass next to it.

"Is this kind of approach recommended in this situation?"
The pilot is allowed to do whatever he deems necessary in the interest of safety. In this case, it sounds like if he doesn't just "aim at the runway only using IRS for guidance" he will run out of fuel and just crash somewhere anyway, so he has to use what he's got.

[what next]

Good morning!

I would say: «If you have the guts to get yourself in this kind of situation, you should also have the guts to die like a man.»

But seriously: In an emergency, every measure that might improve your situation should be considered. But flying a GPS based direct-to course to the airport coordinates while descending to 50 ft above aerodrome level is not going to work in 99 percent of cases. Firstly, the coordinates stored in most GPS units are those of the aerodrome reference point and not those of the runway threshold(s). Second, obstacle clearence off centerline does not even come close to the kind of minimum that you have in mind.

The only chance to survive this kind of situation is to establish yourself on the extended runway centreline (based on the co-ordinates of the runway threshold!!!) early and follow a glide path that will keep you above all obstacles. A so-called "self made non precision approach". The cemeteries are full of pilots and their passengers who messed-up on this kind of approach, even with much better weather than yours. So better don't try it unless it's your only option.

Greetings, Max

[BOAC]

Better than nothing and at least if you crash you will crash near rescue facilities.

Many years ago a forlorn voice was heard over the Bay Of Biscay saying " Everyzing is in fog, I cannot land, I will 'ave to ditch" whereupon someone piped up - "Sorry to hear that, old bean - why not try to crash on an airfield instead?"

So, to answer your questions:

how far will you be away from the centerline? - depends on your equipment/aids - anything between a few feet and a few miles

is this kind of approach recommended in this type of situation? - err - perhaps you could list your alternatives?

[hetfield]

Concerning lateral off-set in such a situation, remember the assistance of nearby ATC units.

The today technologie of this machines is quite amazing.

[David Horn]

Though don't forget that Airbus in Ethiopia whose IRS calculated its position from a badly calibrated VOR, nearly resulting in a messy CFIT incident. Crew were given correct indications from an NDB, but judged it unreliable.

[Piltdown Man]

Firstly, the coordinates stored in most GPS units are those of the aerodrome reference point and not those of the runway threshold(s). Second, obstacle clearence off centerline does not even come close to the kind of minimum that you have in mind.

I think this depends on the aircraft you fly and the equipment installed. I used to fly Fokkers. Some had really smart FMS's which allowed you to fly to runway thresholds, with varying degrees of success and some would take you pretty close(ish). In each case, a reasonable planting on an airfield could be guaranteed but you would have to manage the vertical profile yourself. But I now fly an Embraer and a fit that would allow a very accurate (but not approved) planting on a runway and the beast would manage the vertical profile for you as well (quasi-ILS). Obviously I'd prefer not to be in such a compromising position in the first place, but if I had no other option I'd go where ever I could get the best RFF/runway/weather/obstacle combination (and as few lawyers as possible).

PM

[ab33t]

Yeah I would say use all navigation equipment you have , try and get SARS

[Denti]

If i really have that surprisingly bad day as suggested in the original post, just select any approach that does not require the ILS to be on the air in the FMC and fly it down to 100ft, at that point latest my autopilot will make me aware that i should switch it off (auto-callout AUTOPILOT) and gently float along the runway a 100ft if i dont switch it off. Of course it is not a precision approach, so with the weather described i really do have a problem there, i dont know if an Enhanced Vision System as you can get on business jets would help there, sadly boeing still hasn't managed to certify it on the 737 although they announced it allready in 2002 or so.

If there is a military airfield nearby try to land there, many of them still have GCA equipment and trained ATCOs and they can talk you down until you hit the runway.

[FullWings]

Having flown a fair few RNAV final approaches, I'd say that if it was GPS driven and you had one or other threshold positions, you'd be in with a fair chance of putting it on the runway not a million miles from the normal TDZ.

You could either follow lateral director commands and calculate a glideslope using range/height or quickly bash an approach into the FMC and use vertical guidance as well. Do the flare on the radalt and continue tracking until you stop - should be good for Cat IIIb no DH, if it's that or crash & burn.

It'll certainly contain the wreckage within the airfield boundary where the emergency services can come and get you...

[IndAir967]

Was in a similar situation

Aircraft : C172 With GPS IFR APPROVED
Was instructor on board for IFR Cross country..
Route: Bakersfield CA to Torrance CA

Torrance was reporting 1000 SCT and TAF actually predicted
Broken to scattered clouds for arrival.

Enroute Just over burbank noticed Alternator Failure ..

Instruments Unreliable .. Battery Was Draining Out.
Communication was starting to get scrambeled.

And to add to it Torrance became Overcast ..

Entire Southern California Stretch became OVC and the nearest VFR airports were on the other side of the mountains which themselves rise upto 9000 feet ..

SOCAL vectored me to Final APPR
and infact brought me down until 1000 feet but runway/airfield was not in sight .

I was transfered to Torrance Tower with whom I confirmed that I was on the extended centreline. Tower also informed me that an aircraft which landed before me called in the ceiling to be 700 OVC. So I asked the tower to give me a call about 10 seconds before I hit the 2 DME point.

With some basic calculations I predicted that the Aircraft can safely be at 600 feet when 2 DME out on an approach and decided to go down safely until that altitude.

Tower called me 2 DME Out I started a comfortable 400 FPM descent and entered IMC at about 1000 feet and was out by 650 feet and the runway stood there infront of me majestically lit !

p.s. today i dont get to do these things on the BUS !;)

[bfisk]

This would most definitely be an emergency situation, and as you know, in an emergency you can legally do anything you determine to be the safest course of action. So when the **** is about the hit the fan, you need to do whatever you can to better your chances of saving your life.

But be aware that you are really a test pilot, and all blame will be on you when you crash the thing, because you should not have gotten yourself into such deep **** to start with.