The ILS Approach
 

Looking for some information on the differences between shooting an ILS approach in a helicopter versus a fixed wing aircraft. Also on any difficulties rotarcraft have performing an ILS at a busy international airport.

Any info for a dumb stupid ass fixed wing pilot would be really appreciated!

Biggest hassle is when helo drivers slow way down and chew up more airspace, stacking those starch-wings up behind you. Most ILS are shot at 130K+ by airplanes, so if you use 70 or 80 you really bog down the guys behind you. In an S-76, a 120knot ILS is a nice one, and you always have at least 1/2 mile to burn off the speed at the bottom. If ceiling is really at mins, and the ILS runway has only 1/2 mile to the ramp, then maybe slowing to 90 is better, but for big airports and average conditions, I shoot them at 120 knots.

Also, the higher speed makes it easier to track the beam, since a given bank angle error yields a fraction of the turn rate error, so you can catch heading drifts much faster. Also, the airspeed produces more ROD adjustment, since the power curve is steeper at 120, so plus or minus 5 knots is a fine glideslope adjustment.

Bad Nick, naughty Nick! All us QHIs spend hours nagging at pilots to control height or RoD with lever and here you are saying do it with cyclic - heresey! you'll be burned at the stake!!!

Global Pilot,

The big problem with Helis doing fast ILS approaches is that the speed has to be washed off at the bottom (we obviously can't land at fixed wing speeds, especially if there are skids rather than wheels fitted) which can put the aircraft above the glideslope or even back into cloud if the pilot isn't careful, due to flare effects tending to convert speed to height. Also, in extremely poor conditions, the single pilot has to go from instruments to flying at very low speed or to a hover with marginal visual cues, a "third dimension" that isn't necessary in fixed wing (once the aircraft has touched down on the runway it's a 2D environment).

We are based at a busy airport and often get asked to make "best speed". 130 kts is good for ATC but it does mean that the gear can't go down until late on the approach. Personally, I use the airspeed hold and control the airspeed with the coolie hat and let the aircraft make its own arrangements - it does it so much better than me!

I then "beep" the speed back to get below gear limiting speed and if the weather is right on limits I bring it back to 75 or 80kts to make life a little less hectic over the runway.

I'm with crab on this one Nick.

Control the path on the glide slope with the collective. Especially so with a attitude retention system such as an un-coupled approach with an A/P equipped aircraft.

Also lets remember the Regulations re Speed restrictions. As a helicopter is classified as a Cat A for speeds, a Cat A speed range on final approach is 70 to 100 knots. This still allows for up to 150 knots on the intial and intermediate segments of the approach.

Agree with Geoff regards the CAT A speed restrictions ... but ... I found that if you can shoot the approach faster then the ATC, especially at Sydney and Canberra really appreciate it. Have shot them at 170 in the Seahawk and found that as long as you're slowing down by about 2 to 3 miles on finals, then the maintenance of the glideslope is pretty easy. Not advocating busting the rules at all but I find the CAT A limitations these days a little frustrating....worked well in the days of Hueys though.

Have found that at the higher speeds, Nick's technique provides more accurate glideslope control. Maybe it's a Sikorsky thing.

If you start altering your airspeed on the ILS, regardless of what cat. approach your flying, doesn't this mess up your timing to your MAP should you have a glideslope failure? or do you maintain your KIAS after the FAF until DA/MDA?

Well I guess the bottom line is whatever works for you.

I personally on the S76 fly the whole approach on the cyclic use the trim release (not the fine trim) for adjustments, as I like Nick find that the delay if you use the lever is too long.

I only touch the lever if the speed gets too far out of line from your target i.e. more than 125, or less than 115.

however typically I give the lever a single little nudge down at about 1000' which allows for the increasing air density as you descend which if you didnt do would mean that your speed would be too high at the bottom.

as for the timing by changing speeds it is obviously important if you are flying an NDB from a locator beacon (outer marker), but where the MAP is at the beacon on the airfield or you are flying the ILS down to 200' and as your speed will be within the typical IR limits +/- 5 kts anyway who cares about that ?
(I guess someone will quote from pans ops now)

regards

CF

We always learn things!

Goeff and Ogsplash - Helicopters are ALWAYS Cat A on the approach plate, guys, no matter what speed you fly. That is because you don't have a 1.3 Vso (unless I forgot and left the wings on my helo). The limits to maneuver are meaningless to a direct lift aircraft that is at its best maneuver condition when a starch-wing is teetering at the edge of control. I agree with you Ogsplash, the slow down usually starts much earlier, since you usually break out at 500 or 700 feet, where you are miles away from the turnoff.

Crab - 5 knots of speed at 130 is worth the entire ILS ROD, so a few knots is powerful, and easy. If you juggle the collective, be my guest. I use the first 4 knots for altitude, then back off a little collective.

Lightening_Boy - a few seconds difference makes no real problem, really. If your glideslope fails, you are non=precision, anyway.

Gear speed is a real concern, I agree. If you can't drop your wheels at 130, you are perhaps flying the wrong type, since an S-76 is 130 gear down speed. I do agree that I want the wheels down at the FAF, and if your gear speed is much less, be at the gear speed. It is tough enough at the bottom without hearing that terrible scraping sound!

It is fairly easy to stop a 130 knot helo when at 1/4 mile from the threshold, and you have a further 4000 feet to the tower/terminal, (giving you the much better part of a mile, if you are only visual just as you hit minumums). This uses about 7 degrees nose up attitude for most helos, an easy thing visually. If you can't do this, can I suggest perhaps dentistry? ;-)

Seriously, I use 125 for most ILS and find it very easy, but if you are right at mins, and it is a small airport, and its night, I get down to perhaps 90. I flew several hundred approaches to zero zero during a test program once, and found the precision of localizer glideslope retention much better at the higher speed. The turn rate is based on v squared, so if you are at 70 you have almost 4 times the turn rate for 1 degree of bank as you do at 125. This means your flying has to be more precise to achieve the same nav accuracy, or stated another way, your precious workload is being used to keep sharp bank when it could be helping you maintain other awareness.

Jacking the collective up and down is an easy way to get an unstabilized approach. I also set power and leave it there, and control the glideslope with airspeed. One thing to recall (FAA regs, others I don't know) is that if you reduce the published visibility by 1/2 then you must be at or below 90 kts before the MAP. I often fly at higher speeds and then start reducing airspeed at about 200', but if the weather is really down, and visibility is below 1/2 mile, then the airspeed is going to be 90 or less just about all the way, and screw any fixed-wing behind me. Fortunately I don't have this problem often, and I'm usually the only aircraft on the ILS anyway. But if I have to go to my alternate, which may be a large metropolitan airport, then I'll do what I need to do. We try to accommodate others when we can.

I never time an ILS. If the glideslope fails on the way in, then it's a missed approach and rebrief for the localizer. One brief, one approach, period.

Gomer Pylot

"I never time an ILS. If the glideslope fails on the way in, then it's a missed approach and rebrief for the localizer. One brief, one approach, period."

Just out of curiousity, why is that? Wouldn't it be just as easy to brief the approach with the MDA as well and just hit the timer at the FAF?

BTW, I'm no expert, sitting my IR next week hopefully!!!!

Ogsplash and Geoff are referring to the Oz regs which is supposedly a pans ops reflection, but I must admit I interpret them differently. The wording is from AIP, ENR 1.5 - 2 para 1.3.1 (b):
"where helicopters are operated similarly to aeroplanes, they may be classified as CAT A"

I read the critical word as "may", not must, shall, or will. In otherwords, when doing an instrument approach such as the ILS in the 212, then CAT A is beaut. But in the BK117, when I want to do 120 kias down finals (which, like Nick I also prefer) then I simply use CAT B minima requirements. If I feel I need the CAT A minima (almost never different in Oz to CAT B) then I limit finals speed to 100. I think this is reasonable given the wording that says I "may" operate as CAT A.

As for attitude Vs collective for glideslope, it depends on the machine/situation. Using attitude to correct for glideslope in the 212 can lead to VNE, and using collective to come up at 145kias in the BK can lead to overtorques!! Nick's 4 kts is a good idea, and I'll try it next time - thanks.

In answer to the original question, I think it is easier to shoot an ILS in a helicopter than a fixed wing, and I think from the subsequent discussion you can see that it is far more flexible with far more options.

Which is all well and good if you're flying manually, but the autopilot does it with cyclic. Well ours does. Are there any autopilots that control height with collective?

Mighty Gem, yes there are; those that are 4 axes. On the 155 the collective is coupled when using vertical functions on their own, but with the IAS below 60 kts (ie ALT, V/S or G/S ) or when the IAS and a vertical function are coupled together. If above 60 kts and a vertical funtion is coupled but not the IAS, then it uses the cyclic to control that function, and effectively the collective becomes a speed controller.

When fully coupled on an ILS it has to be seen to be believed; you can merrily beep the IAS from 165 to 30 and then back and the needles don't budge at all. It will then take you all the way down to 25 ft and 30 kts down the centre of the runway, hands off (well, lightly guarding the controls, perhaps!) On top of that, it has no gear limiting speed, which is a bonus.

I'm surprised by how many people advocate glideslope control using cyclic, especially the 76 drivers; I always thought it was delightful to hand fly accurate ILS' with its PBA. An accurately trimmed aircraft in smooth conditions needs very little cyclic input and just small, smooth, collective inputs, usually. If, however, you then factor in a bumpy approach, what are you using the controls for (those that advocate cyclic for glideslope)? Do you still keep the glideslope with cyclic, but accept bigger speed variations, or do you adjust the collective to reduce the speed variations, or do you move everything and adjust both speed and glideslope with a combination of both inputs? If you stick to the primary effects of control, the principle doesn't change; you still maintain the IAS with cyclic and the glideslope with collective, you just need more frequent and larger inputs.

One advantage of our flexibility with IAS is that by keeping it high in the initial stages of the approach we can minimise the wind's drift, then by reducing it in the final stages we can remain within the rapidly constricting cone more easily.

Was once asked by ATC to "slow down" behind an Airbus A320, which brought a smile to my face.

I'm totally with Nick Lappos on this one. Every IFR helo I've flown is easier to fly the approach with the stick. Set a ball park power setting as the glide slope comes in and then use the stick to the bottom. I've used this on S61, S76, AS332, AS365 and the355. All behave the same when using this technique.:)

My preference is Nick's technique, especially in the very stable S76. Although I hear that dropping the airbrakes at the OM is pretty good for final speed control ;)

I hoped to try a couple of ideas this afternoon, but the IP with me thought it more fun to take off the pri hyd (no T/R assist), then the No 1 engine, then a running landing :rolleyes: At least the 109 Power with the new tail rotor blades is quite benign hydraulics off, compared to the "old" blades :)

I am basicly a S76 driver and I always prefer controlling glideslope with cyclic. Way back in my basic IR I was thought to do it with collective, but soon found out cyclic worked better for me. And actually, when flying as an instrument instructor and see pilot hand fly an ILS with collective, they normally do a much better job when doing it again with fixed power setting. It is just one less thing to work with in IMC, and doing it in IMC is really the diffrence.

On the S76 35-40% tq for ILS is a good baseline that works for most of the time, will give 120 with gear down.

An S76 with Phase 3 is the only one I find it better to adjust glideslope with collective since it is so stable in attitude and speed.

To be honest, I do not think a 4 axis AP flies glideslope adjustments with collective, it maintains airspeed with collective (or slows it down in decel mode) and follow the glideslope with cyclic (pitch actuator). Somebody might be able to confirm/correct this.

To me it seems that most Bell pilots want to fly the glideslope with cyclic. Also for UK pilots it seems to be the prefered choice. Have no idea why in both cases.

Anyway whatever works for the individual with the least workload must be accepable:ok:


CB (hiding for flak).

Lightning, it's a different approach, with different minima, and different requirements. Trying to salvage an approach when things start going wrong can be very dangerous, and I want to live to fly again.

Thanks for that, 212Man.

I was told tonight(during the IF phase of my 6 monthly check), that here in the UK you should use the collective. Certainly during an IRT as using the cyclic will put you outside of the +/- limits for speed, resulting in a fail.

Flying the ILS with cyclic in Oz also has another ramification: and adjustment of 10 kias, or 10% which ever is less, shall be notified to ATC. Also, I wonder what the efeects on preceeding/following traffic would be, but I suspect it is minimal given seperation standards.

Collective Bias, I suspect your comment of most Bell pilots flying the cyclic could be reworded, as I find it is most Jetranger pilots - but not Huey pilots. They tend to get in the habit of setting top of the green and flying altitude with cyclic in the cruise, whereas in the Hueys (except 412), doing this would result in a significant VNE exceedance. Given alot of guys have flown jetranger first, it is a habit that needs to be sorted out in the huey transition.