Min visibility for departure in LVO's

[fart]

I wonder if you can share some information on the minimum required departure visibility in Low vis operations.

Recently our CAT II has been downgraded to CAT I due to LOC interference and I was just wondering if that would chnage the min vis requirement for departing aircrfat from the airport in low visibility conditions. In a CAT II situation, the min required vis was 125 m and if the TD RVR fails, then it increases to 150 m and both mid point and stop end RVRs must be serviceable for a rejected take-off. Now, in a CAT I situation, the normal RVR for landing is 550m and I must assume that in order to depart safely, the min departure visibility must be 550 m in the event that the crew has to return for an immediate landing after take-off in an emergency. If the dep. vis is less than 550m and you are allowed to depart, does it require a take-off alternate which must be within a short distance/time away?

Do you expect controllers to protect the ILS sensitive area when the vis drops below 600 m and 200feet? Our CAT I holding points are within the sensitive areas and the question is whether it is permisable to hold aircraft at the CAT I holds when there is arriving aircraft on the approach? Using the CAT II holds will obviously take care of the situation, but it requires additional spacing on final between arrivals in order to get a departure away. You are probably looking at a min 15 nm in trail distance between arrivals if a departure is inserted in between arrivals.

Any information on low vis ops would be appreciated.

Thanks

Fart

[Pilot Pete]

fart

Quite right in your assumptions. If you need to make an LVO approach you need to check with ATC that they have LVO's in force to ensure protection etc. So it follows that you would not want to be making an autoland in LVO conditions if ATC were still using the CAT I holding points.

You are also correct in thinking that the spacing is increased significantly in LVO conditions (any ATCO's got the exact gen?) and delays are to be expected so make sure you have plenty of fuel for going round in circles at your destination should the forecast be bad. It's also worth considering your strategy when you get to the overhead and enter the hold. ATC will generally give you the expected delay in the hold, if that is going to put you close to a diversion decision then it may be worth diverting early, getting into your alternate and re-fuelling with plenty (golden rule; don't tech stop and end up diverting again because you didn't put enough on!) of fuel then race back to your original destination which is now less busy because everyone else has now diverted to where you've just been! Happened to us once going into Manchester early morning with no low vis forecast but LVP's in operation when we picked up the ATIS. Every man and his dog entering the stack (all with the same forecast as us so no-one had much fuel to be playing with) and we diverted before even reaching Dayne, refuelled at Brum as everyone else followed us in, departed and landed at Manch probably 30-45 mins before the next one!

125m is our absolute minimum as you point out the same rules apply for RVR reports. The reason for a departure alternate within a certain distance (I've flown with a couple of outfits now and one used 400nm and the other 250nm) is not down to ILS category primarily, more to do with worst case, i.e. engine failure on T/O which precludes an autoland (on the 757 you can only autoland with one engine if you have armed 'approach' prior to losing the engine), but that does lead to some debate on is it wiser to fly possibly a considerable distance to an alternate on one engine when you have a perfectly serviceable airfield in LVP's nearby (don't shoot me down I didn't say I'd do it, just there is a debate about it!). So even if the ILS was CAT III we couldn't make an approach in the EFATO case.

Hope that helps......there's tonnes more for a winters day reading!

PP

[fart]

Pilot Pete,
Thank you for the info - it is indeed very helpful.

Regarding the spacing on final, and by the way, I am not from or working in the UK, our spacing criteria is as follows: (Somewhere in ME)

30 nm in trail between arrivals if there is a departure in between.
20 nm in trail with no departures.
Parallel runway ops suspended.
Arriving aircraft must be established (vectored) outside 10 nm from TD at a speed not above 210 knots.
Departing aircraft must have crossed the LOC antenae at the upwind threshold before the arrival reaches 10 nm from TD.
Approach ban policy - need 350 m RVR at 1000 feet for CAT II approach.
Runway incursion alarms active (GMR/SMR)
etc.

cheers
Fart

[GlueBall]

I think that you are mixing apples and oranges. Departure minimums have nothing to do with landing minimums. The only criterea when departing from an airport that is below landing minimums is to include a "Departure Alternate" for planning purposes. Unless an airport operator specifies higher departure minimums, our Ops Specs allow us to depart with 600 (feet) RVR, provided that runway centerline lights are operative and that at least two out of three RVR detectors are operative. Our Jeppesen airport charts include FAR 121 takeoff minimums for each runway.

[Pilot Pete]

Glue ball

See what you are saying and departure minima have nothing to do with landing minima, but you say

The only criterea when departing from an airport that is below landing minimums is to include a "Departure Alternate" for planning purposes.

which is not strictly true as with a minimum departure vis of 125m RVR and a CAT IIIb approach minima of 75m the airfield landing minima could be less than the departure minima, thus the criterion for the departure alternate is more about conditions precluding a return to that field i.e. worst case including technical problems such as single engine, as mentioned above on one engine we could not do an autoland if the engine failed before arming the approach mode. So no, minima for approach and departure have no comparison, but if you are going to depart you need to know where you can go if you should not be able to return.

PP

edited due too much cabernet sauvignon

[GlueBall]

Our FAA Ops Specs criteria for a "Departure Alternate" is that the airport is within 2 hours cruise (still air) with one engine inop. If that condition cannot be met, then obviously takeoff is not permitted...until an airport within two hours cruise in still air (including the airport of origin) meets alternate landing weather minimums.
I think what you need to keep in mind is that a minimum visibility takeoff is not predicated on being able to immediatley return to the point of departure. I have departed many airports many times in weather conditions that precluded a return in case of an engine failure.

[BlueEagle]

On the B747-400 I flew we had a PVD display, (a black and white barbers pole), on the coaming, centrally in front of each pilot.

The PVD requires a useable ILS localiser signal that has to be selected prior to take off. When the aircraft is on and pointing down the runway centreline the display will be stationary.

During the take-off roll, the PVD will provide centreline guidance when the aeroplane exceeds 2.5 degrees or greater deviation from the runway centreline. The display moving to the left is a command to turn to the left and vice versa, the faster the display moves the larger is the command.

This equipment allowed to take off when the RVR was down to, but not, below 100 meters.

[Pilot Pete]

Interesting Blue

Was the slant view from a 747 cockpit worse than for a smaller type ie. 737? I mean was it possible that a 737 pilot would be able to count half a dozen centreline lights whereas you would be able to see less in the same conditions? Was this a reason for the PVD or was that just to get your minima down to 100m? What was minima for T/O without the PVD?

PP

[BlueEagle]

View from cockpit of 747. It was not as good as from a 737, for sure. Our landing minima DH for Catlll was 20' whereas the 757/767 would be 0'.

Reason for PVD. Not all operators have the PVD fitted but I am guessing that it was originally intended to get minima down to RVR 100' as the T/O minima otherwise would be as published in the Jeppeson.

[m&v]

Pilot pete,yes you will get the scenario whereas the 'landing'vis is lower than the T/o vis-due to the theory that the Fed's give more leeway to a Dynamic situation than the static situ (on the ground)
One needs a certain RVR for T/o,as stipulated by the Ops spec.
namely 600'-1200'feet (north america)depending on the airport/runway lighting and equipement.If the weather is on Minimums for T/o-one needs a T/o alt(within 1 hour twins/2hours more than twin)...That having been said ,one can always return in the event of EMER'on a CAT3 arrival(Sim practice heart attack etc).If the CAT3 goes bust,then the Cat 2,or the Cat1,with the required increase in RVR,is required for the return.
Basically 600 rvr for T/o needs Centre line lights/markings-if no centre line-1200 applies:rolleyes:

[Pilot Pete]

Blue

Thanks for the reply, interesting reading.

m&v

I think we are saying the same thing in a roundabout way. Here in the UK with my Ops Manual we can depart down to 125m RVR with certain a/c, crew and airfield requirements met. If the airport is CATIIIb operational then we could undoubtably make an approach to minima if we required to return to the field using the published CATIIIb minima (usually 0' or 14' DH and 75m RVR), but only, and this is the point I was trying to make, if the a/c, crew and airfield were to meet the operational minimal requirements. It therefore follows that the T/O alternate has nothing to do with the departure minima but is there when a return to this airfield is precluded due to downgrade of equipment meaning that the revised minima would not get us back in; the example I used was in the EFATO scenario where we could not make an approach to autoland if the engine had failed before arming the APPR mode, therefore a suitable departure alternate is required within a certain distance/ flight time with weather conditions forecast as good as or better than the required minima dependant on the approach aid to be used at that field.

Phew, hope that clears my feelings up on this matter!

PP

[Sick Squid]

...another little issue to consider... there should be a limit somewhere in your ops manual for take-off below which LVP's must be in force... 400m for my company.

To go down to our absolute minimum (150m/125m) requires protection.. quite why when the PVD is not required for that I don't fully understand (apart from the in-trail landing/departing aircraft consideration) but there you go.

With planned Cat 3a single engine capability, you really have to go some to lose the return option close to Take-off minima at most major fields. But as others stated better than I, they are two completely seperate calculations.

Sick Squid

[m&v]

Agreed PP
The whole concept of the Dept Alt is becoming deemphasised these days with the autoland/eng out capability of the fleet types.The only case is total power failure at the Dept field(aux should kick in),thunder storms,or strong winds etc.
The concept seem's to be an 'olde' holdover from the Cat1 days.

Cheers :D

[Pilot Pete]

Sick Squid

Got me looking for the RVR limit below which LVP's would have to be in force for departure but could not find one specified anywhere. I would therefore assume that if I were to depart with less than CAT I RVR approach minima then LVP's should be in force?

You also mention CAT IIIa minima allowing return on one engine. Does your type allow for a planned autoland in the case of an EFATO? That I find very interesting as the 757 does not allow for this.

Could your required 'protection' when down to absolute departure minima be anything to do with ensuring you line up on the centreline by reference to the localiser?

PP

[Spitoon]

As a controller I can't really comment on Ops Manual procedures but bear in mind that here in the UK LVPs can involve far more than just using CAT III holds. Many other restrictions are introduced to limit the number of vehicle (and sometimes aircraft) in airside areas and often to physically block runway access points that will not be used. At airports that do not have surface movement radar it is common for movement on the manoeuvering area to be limited to one at a time. These procedures are intended to prevent unauthorised runway incursions but may also be taken into account by the Ops Manual.

[m&v]

Yes'
the A320's good for an auto land on one engine,although for a long time 'local' fed's disallowed it.In Canada still different 'approvals' for different Co's.
In Catt3 ops the engine has to be 'secured'and checks complete at least 1000' agl.....:eek:

[BusBoy]

A330 with Para-visual Indicator (PVI) which requires valid LOC signal for departure runway allows 75m RVR for departure.