Rotorcraft Flying Handbook - Normal / Steep Approach

[Collective Down!]

I'm working on my CFI helicopter rating and I've had this question since the days of my private training...

 

The rotorcraft flying handbook says that a normal approach angle is 8 to 12 degrees, and a steep approach is 15 degrees. When you work out the math, and calculate the required rate of descent at 60 knots (approach speed in the R22) you get a rate of descent between 845 fpm and 1260 fpm for the normal approach. 845 fpm isn't too difficult to achieve, but I wouldn't consider that a "normal approach."

 

In the case of the steep approach (15 degree approach at 60 knots) you should be doing 1570 fpm according to the math. For those of you that get hurled at the ground in the doulbe deuce every day, you know that a 1500 fpm descent in the R22 is only possible during a straight-in auto.

 

So what gives??? Who wrote this book? I understand that the RFH is a compilation of well accepted techniques, it's written by the industry, and accepted by the FAA and yada yada... I also know that 90% of you are thinking "The RFH is not applicable to each helicopter model, and you have to follow the manufacturer recommendations." Well, before you fire back with that response, if you brush the dust off your Robinson R22 flight training guide you'll see the same thing as the RFH (10 degree normal approach, 15 degree steep approach).

 

I have been teaching in fixed-wings for a while now and I always preach adhering to the FAA recommendations and the manufacturer recommendations both for safety and CYA reasons. The latest version of the Airplane Flying Handbook (FAA Book) is near perfect, but the RFH is more difficult to teach from and could use a ton of improvements.

 

So my question is: Has anyone noticed this before? How do you explain this to your students? Does anyone actually do a stabilized approach this steep (from 300 feet AGL per the RFH) in other types of helicopters?

[justfly]

You're kidding, right?

 

Assuming (ass-u-me) you're not trolling... <_>

 

They're NOT airplanes, helicopters do not maintain constant airspeed nor descent rate on approach to land. (how bad did you scare your instructor?? ) It is a constantly descending/decelerating approach so that, "The approach should terminate at the hover altitude with the rate of descent and groundspeed reaching zero at the same time.".

 

The approach starts at the recommended (60 KTs for the R22) airspeed and approximately 300 feet AGL, but not for long; the speed/descent rate will continuously decrease during the approach. After lowering the collective to initiate the deceleration/descent you will need aft cyclic to maintain the recommended approach airspeed attitude, not approach airspeed.

 

Did I bite the hook sufficiently , or did I completely misunderstand what you were asking?

 

(hmmm, I wonder why Frank wrote Safety Notice SN-29??? )

[HH60Pilot]

You're kidding, right?

 

Assuming (ass-u-me) you're not trolling...

 

They're NOT airplanes, helicopters do not maintain constant airspeed nor descent rate on approach to land. (how bad did you scare your instructor?? ) It is a constantly descending/decelerating approach so that, "The approach should terminate at the hover altitude with the rate of descent and groundspeed reaching zero at the same time.".

 

The approach starts at the recommended (60 KTs for the R22) airspeed and approximately 300 feet AGL, but not for long; the speed/descent rate will continuously decrease during the approach. After lowering the collective to initiate the deceleration/descent you will need aft cyclic to maintain the recommended approach airspeed attitude, not approach airspeed.

 

Did I bite the hook sufficiently, or did I completely misunderstand what you were asking?

 

You mean you don't maintain 60 knots until touchdown?? Maybe that's why I keep spreading the skids on landing!

 

You are correct, 60kts on entry with a/s and rate of descent decreasing until touchdown (or termination in a hover).

 

Doug

[Collective Down!]

(hmmm, I wonder why Frank wrote Safety Notice SN-29??? )

 

Another victim of lead paint... What a shame.

 

I'm a CFI applicant (and ATP for God's sake), do you really think I fly 60 knots all the way down?

 

If you look at the math (which you obviously don't understand), you'll see that no one flies a normal or steep approach at the angle the book says to AND THAT IS EXACTLY MY POINT.

 

For the case of the steep approach, it says to intercept the 15 degree approach angle at 300 feet AGL. If you're going 60 knots, it would take 1,500+ fpm... that's what it would INITIALLY take to fly a 15 degree descent angle at 60 knots. When you slow to 30 knots, you're descent rate would be half that (about 750 fpm). When you slow to 20 knots, you'd be descending at 500 fpm (according to the math).

 

I'm not advocating 20 knots and 500 fpm descent.... I'm saying that the RFH may not be written correctly.

 

(My figures assume no wind, and sea level ISA conditions, of course... Wind would be on your side, but altitude would work against you).

 

Here's another example for the steep approach. Cross the threshold of the runway (with instrument markings) at 260 feet AGL, and follow a constant angle of descent to terminate in a hover at the 1,000 foot markers....

[Eric Hunt]

Another good reason why my country doesn't have 150 hr pilots trying to teach.

 

You don't start a steep approach at 60 kt.

 

You fly the circuit to your normal approach profile of maybe 4 degrees, but hold height and slow down until you see the steep profile appear. You might be back at 40 kt by then, maybe less. Commence descent, and reduce speed as you go. Simple.

 

Before you start squawking, yes, you will be inside the Avoid Area chart for part of it. But you are only doing the steep approach because the situation requires it, right? Otherwise you would fly a normal approach and stay clear of the chart.

[Pogue]

Looking through the Rotorcraft Flying Handbook I don't see 60 knots mentioned anywhere in the description of either a steep or normal approach. I'm only a rookie but when I intercept my normal glide slope at 60 knots and 300' AGL I lower the collective till I'm staying on my angle, and I really don't care what the initial rate of descent is. Since I'm also slowing down as I approach it takes care of itself. We try to intercept a steep approach at about 45 knots which also seems to work just fine. Being the ham fisted kind of student I am, I have done steep approaches starting at 60 knots, and yep, the collective goes pretty much to the floor to get the descent established. But again, once the speed is under control, so is the descent rate. So I guess I don't understand your point. It seems like you're implying constant speed.

 

And I only eat latex paint, so it ain't lead.

[Gomer Pylot]

What I do for a normal approach is to start at about 300 feet above the touchdown point, and in many models I try to hit that altitude and about 60 kts, decelerating. I adjust the controls to get about a 300 fpm descent, and keep the approach angle constant. I don't care about airspeed, just rate of closure. I've made approaches with 50 kts of wind, and with zero wind, and the airspeed is dramatically different between them, but the groundspeed and rate of closure are the same. The reason for the 60 kts is that it is somewhere near the minimum rate of descent, and thus requires the least power, for many light helicopters. The model I usually fly is slick, and Vy is 75 kts, so the 60 kts is really moot. I eyeball the approach speed before descent, and then put the pitot tube on the far edge of the helideck and keep it there, with no more than 500 fpm descent, and I prefer less.

 

I'm not sure where you're getting your rates of descent, but they're far too high for a safe approach.

[Collective Down!]

Holy cow... Please read the post a little more carefully... I AM NOT ADVOCATING A STEAP, HIGH DESCENT RATE APPROACHES. Yes, Gomer Pylot I AGREE WITH YOU ALL THE WAY, those rates of descent are way too high to be safe. THAT IS MY POINT!

 

The RFH says to intercept a constant descent ANGLE, and the rates of descent that I listed are what would be required in order to get those descent angles. And in turn, my point is that no one flies a descent angle that steep (for good reason). I am not saying that no one does it right, I'm saying that the RFH has some crazy descent angles in it, that are nearly impossible to achieve, and are unsafe to attempt. You are all agreeing with me without even realizing it.

 

Eric Hunt, you're openening a whole new can of worms saying that a normal approach avoids the H/V curve and the steep approach does not... Neither the normal or steep approach avoid the curve, but that doesn't matter, because the H/V is meant for the takeoff profile, and does not necessarily apply 100% to the approach and landing due to the lower collective settings during that phase of flight. Do some more research before you make more grumpy faces at me. By the way, you did a pretty good job jumping to the conclusion that I only have 150 hours...

 

The RFH does not say to start the steep approach at 60 knots... I'm referring to the Robinson R22 Flight Training Guide... it says to intercept the 15 degree approach angle at 60 knots and 300 feet AGL (if you're flying an R22) <-- I felt the need to add that for a few of you.

 

For those of you wondering where I get the ROD numbers, it's math (trigonometry). If you don't trust my math, go to the last page of any instrument approach chart booklet. Those numbers on the left column are descent angles, with associated rates of descent as you go across for different ground speeds.

 

If you are descending on an 8 degree approach, in order to MAINTAIN THE EIGHT DEGREE APPROACH ANGLE, as you slow through 30 knots GS, you'd have to be descending at 425 feet per minute (for just that instant that you're at 30 knots). Ask yourself... Is that approach steep? You bet it is. But the RFH says that a normal approach has a constant angle of descent between 8 and 12 degrees.

 

Read this carefully... I DO NOT GO OUT IN MY ROBBIE AND DO THIS. What I am VERY SIMPLY saying is that, no one descends at the angles specified in the RFH, so why doesn't it get changed?

 

Why don't we consider a normal approach to be say, 4 degrees. And a steep approach, about 6?

[relyon]

... So my question is: Has anyone noticed this before? How do you explain this to your students? ...

Your observations are correct. I've done the same math and come to the same conclusions. Regardless of what is published in the RFM and other sources, the shallow, normal, and steep approach angles so often referred to as being at 5, 10, and 15 degrees, are actually around 4, 6, and 8 degrees. On a normal approach in calm conditions, I find my rate of descent to be be very close to 1/10th of airspeed (i.e. 60 kts has a 600 fpm descent rate, 50 kts a 500 fpm descent rate, and so on) - just under 6 degrees.

 

At this point, I think it would take an act of God to get the helicopter training industry and the FAA to acknowledge the reality of the situation and change the way things are taught. They know what those angles are and no one is going to confuse them with facts when their minds are made up. I explain it to my students by telling them what's actually happening, but that they should be prepared to give the published explanation, even though it's wrong. It's more important to pass the practical than to be technically right.

 

Bob

[joker]

CollectiveDown,

 

Eric Hunt's reply hits the nail on the head...for a steep approach you should be much less than 60kts at intercept.

 

I'll try to explain.

 

Your numbers are probably right....however, you are neglecting the fact that as soon as you lower the collective, your airspeed will drop.

 

Thus, at any time on the 'glideslope' you will never be 60kts 845fpm. If you did actually lower the collective exactly at the 12-15 degree intercept point, then you will overarc! The descent must be initiated before interception, as must the deceleration from 60kts*.

 

*This thread prompted me to get out my Rotorcraft Flying Handbook, to find the phrase where it suggested to intercept at 60kts? - I couldn't.

 

What it says, is be aligned at the recommened approach airspeed. Who's to say that that is 60kt? Infact, my 'reccommended approach airspeed' for a steep approach would be more like 45kts.** Try running that through your calculator and you'll find it looks more realistic.

 

GomerPylot has it right when he talks about rate of closure.

 

When I taught this stuff, I would teach 60kts is my pattern speed, and setup speed. However,when the desired approach angle is nearing, you should forget airspeed, and think rate of closure instead. To help people visualise this, you talk about 'apparant' rate of closure. We've all looked out of the window when we are in a jet, and thought how it looks like we are going so slowly over the land, but we know that really our ground speed is very fast. That's what I call 'apparant' ground speed.

 

**For the normal helicopter approach speed, that would be a "brisk walking pace", for a steep approach it is a, "slow walking pace." The airspeed could be anything, depending on the wind, but the rate of closure remains the same.

 

Now at 300 feet, a brisk walking pace just so happens to be about 60kts. Therefore for a steep approach, as the angle is nearing, my speed is already coming back, so that I intercept at a 'slow walking pace' (less than 60kts). So at the 'interception point' my airspeed is significantly less than 60kts, and thus my ROD is less.

 

At first, it is difficult to judge how early to start desceleration and when to start descent. As the pilot get's more proficient, the transition from pattern speed (say 60kts) to being on the glideslope with a slow walking pace becomes smoother. A really proficient pilot can make this transition almost seamless, so to the observer, it would seem that he did intercept at 60kts.

 

What about descent rate? Well, if the 'apparant' rate of closure is managed, and so is the 'constant' angle, then ROD will take care of itsself. The only time you need to watch RoD vs IAS is if you have overcooked it, and need to dump altitude at low airspeeds.

 

INDICATED AIRSPEED MEANS NOTHING FOR HELICOPTERS ON AN APPROACH!

 

Strictly speaking therefore, I guess the only improvement the RFH (and Robinson R22 Flight Training Guide)could make would be to make clear that speed reduction and descent would usually start just before 'glideslope' intercept, or else you'd always overarc!

 

Reylon

 

I think your numbers are on the 'shallow' side for the industry. You say you are finding that your normal approach works out at about 6 degrees. Yes, that is probably what I used to do / teach. I used to stiffen up, when I instructed old-bold pilots, who seemed to me that they still thought they were coming into a hot LZ in Nam. Way too fast and way too steep for my liking.

 

However, looking back on it, I realise now that is shallower than most other areas of the industry. Having moved out of flight training, it is obvious that most people are teaching approaches shallower than they need to be. Why? I think it is because there is more margin for error. The landing site probably has a bearing too. Also the larger the aircraft, the less worry about SWP. (SWP is almost impossible to get in an S76...needs more than 1000fpm descent rate!)

 

So what I am saying is that 8-12 is probably closer to the industry norm, but shallower is usually taught. Maybe some others (not in flight training) would care to coment on this.

 

BTAWTFDIK!!!

 

Joker

[Gomer Pylot]

Rate of descent has nothing to do with trigonometry. You can descend at a 90 degree angle at any rate of descent you want, settling with power ignored, and you can descend at a 45 degree, or any other angle you like, at any rate of descent you like. Angle of approach and rate of descent have nothing to do with each other.

[Collective Down!]

Rate of descent has nothing to do with trigonometry. You can descend at a 90 degree angle at any rate of descent you want, settling with power ignored, and you can descend at a 45 degree, or any other angle you like, at any rate of descent you like. Angle of approach and rate of descent have nothing to do with each other.

 

 

I'll refer you to one of my previous posts... Take a helicopter out and make an approach that crosses the runway threshold at 258 feet AGL, then continue the approach to reach the 1000 foot markers in a hover.... There is no argument about it, this profile describes a 15 DEGREE approach, and that is where the trig comes in. (There are very few other ways to actually measure the angle of approach). Fly whatever airspeed and rate of descent you feel like flying, it doesn't matter... What you'll find is that 15 DEGREES is awfully steep and difficult to achieve safely. In addition, it's hard to do this on a stabilized 15 degree glidepath all the way to the touchdown point (notice I didn't say maintain an AIRSPEED or ROD all the way, I said ANGLE of descent).

 

My argument (that the published angles in the RFH are not practical/safe/etc.) is not misunderstood by the local FSDO. I have a close friend who is a DPE in the Orlando FSDO area that agrees with me 100%. Additionaly,a couple weeks ago I had lunch with a FAA inspector that does the R22 recurrent rides for the DPE's and we discussed the same topic... He also agrees that the angles listed in the RFH are a little high, and difficult to achieve in most helicopters, using recommended techniques.

 

---------------------------------------------------------------------------------------------------------------------------

My suspicion is that the approach angles, at one point or another, were misinterpreted... DEGREES was probably confused with PERCENT GRADE

 

For instance:

 

15 DEGREES angle was probably confused with a 15% gradient... Completely different.

 

15 DEGREE angle would cross the threshold at 258 feet if you were aiming for the 1000 foot marker...

 

On the contrary, a 15 PERCENT approach would mean you'd cross the threshold at 150 feet if you were aiming for the 1000 foot marker... This actually results in about a 7 DEGREE (ballpark) approach angle.

 

In other words, a 15% gradient/angle is one which the vertical rise is 15% of the horizontal run.

 

If any of you live in the central Florida area and want to take the discussion to the skies, I'll provide the helicopter...

[Pogue]

I'll refer you to one of my previous posts... Take a helicopter out and make an approach that crosses the runway threshold at 258 feet AGL, then continue the approach to reach the 1000 foot markers in a hover.... There is no argument about it, this profile describes a 15 DEGREE approach, and that is where the trig comes in. (There are very few other ways to actually measure the angle of approach). Fly whatever airspeed and rate of descent you feel like flying, it doesn't matter... What you'll find is that 15 DEGREES is awfully steep and difficult to achieve safely. In addition, it's hard to do this on a stabilized 15 degree glidepath all the way to the touchdown point (notice I didn't say maintain an AIRSPEED or ROD all the way, I said ANGLE of descent).

 

Ok, I see what you're getting at I think. Yes 15 degrees is steep. I don't find it particularly difficult to stay stabilized on that glidepath, though. But I think you're confusing your point - Forget all the talk about rate of descent and approach speeds, you're real statement is that what a student is generally taught as a normal or steep approach is much shallower than the definition of a normal or steep approach, right? If that's the point I agree with you. If you're saying a steep approach is unsafe, well, yes, you're in a bad part of the H/V diagram for a while, but isn't that capability what makes helicopters useful?

[relyon]

What it says, is be aligned at the recommened approach airspeed. Who's to say that that is 60kt?

The R22 POH states "Make final approach into wind at lowest practical rate of descent with initial airspeed of 60 knots." (p 4-12). The 300C POH states "Slow airspeed to approximately 60 mph for a normal approach and reduce collective for desired rate of descent" (p 4-20).

 

Infact, my 'reccommended approach airspeed' for a steep approach would be more like 45kts.** Try running that through your calculator and you'll find it looks more realistic.

A 45 knot initial approach airspeed on a 15 degree steep approach works out to roughly 1200 feet per minute. The whole point being made here is regarding ANGLES, not airspeeds or rates of descent.

 

I think your numbers are on the 'shallow' side for the industry. ... However, looking back on it, I realise now that is shallower than most other areas of the industry. ...

I can't speak to what other areas of the industry are doing, but the discussion is about what's in RFH and that means flight training. Next time you're out, do exactly what Collective Down! suggests, cross over the threshold at 258 feet and look at the 1000 foot markers. That's 15 degrees at any airspeed or rate of descent, and much steeper than is being taught for steep approaches.

 

Bob

[Bristol]

SNIP SNIP

 

 

If any of you live in the central Florida area ......

 

 

'Collective Down!',

 

I Live in Daytona (training at Tomlinson Aviation). Just wanted to say hey...

[Gomer Pylot]

I agree that 15 degrees is too steep for most approaches. There are times when that is necessary, but not under normal conditions. Perhaps the requirement for that profile is to see that the student can do it, for use in very small confined areas with high obstacles. There are models which make such approaches difficult if not impossible, because you can't see the landing site at those angles. The S76 certainly comes to mind, because it has very little visibility forward and down. In fact, on normal approaches the non-flying pilot is generally completely blind to the helideck, raising the pucker factor a little with a new cojo doing the flying. 10 degrees is barely doable. With other models, though, the steeper approaches are possible, but not something that is normally done.

[joker]

The R22 POH states "Make final approach into wind at lowest practical rate of descent with initial airspeed of 60 knots." (p 4-12). The 300C POH states "Slow airspeed to approximately 60 mph for a normal approach and reduce collective for desired rate of descent" (p 4-20).

 

Reylon,

 

Precicely! These are for 'normal approaches'. But this thread is talking about 'steep approaches'. It stands to reason that the 'recommended approach speed should be different for the different approach...doesn't it?

 

Next time you're out, do exactly what Collective Down! suggests, cross over the threshold at 258 feet and look at the 1000 foot markers.

 

I will go and do that, just for interest. We usually start from 400' above the helideck, but I don't know what distance. It'd be interesting.

 

The whole point being made here is regarding ANGLES, not airspeeds or rates of descent.

 

This was not how CollectiveDown's first post appeared (and the subsequent few), when he was talking about the RoDs and the dangers of.... Actually, Bob I think the thread has now shifted to being about angles.

 

On the angles issue, well, I concede that I haven't worked them though exactly. From your numbers then, and CollectiveDowns comments, it would seem that the RFH and the R22 POH are right out! I'll look into this further, as I can't believe that such a discrepancy would go un-corrected for so long, by so many people!

 

The fact still remains though, that the approaches that I taught (and that most people taught) are shallower than I've seen outside of flight training.

 

Joker

Joker

[relyon]

Reylon,

 

Precicely! These are for 'normal approaches'. But this thread is talking about 'steep approaches'. It stands to reason that the 'recommended approach speed should be different for the different approach...doesn't it?

 

Joker

The Robinson POH does not mention the type of approach, but approach speeds are not the issue. It's the approach angles as mentioned in the RFH for both normal and steep approaches (8-12 and 15 degrees, respectively in the RFH) that are being discussed. The published angles are in excess of the actual angles being flown, and that's the point being made.

 

Once again, fly over the threshold at 176 feet AGL (a 10 degree "normal" approach) or at 268 feet AGL (a 15 degree "steep" approach) and maintain a constant angle to the 1000 foot markers. Do this in any type at any approach speed that suits you, and let us know your impressions.

 

Bob

[Collective Down!]

The fact still remains though, that the approaches that I taught (and that most people taught) are shallower than I've seen outside of flight training.

 

That's partly what I wanted to know... If anyone in the industry actually flies approaches this steep.

 

 

 

The Robinson POH does not mention the type of approach, but approach speeds are not the issue. It's the approach angles as mentioned in the RFH for both normal and steep approaches (8-12 and 15 degrees, respectively in the RFH) that are being discussed. The published angles are in excess of the actual angles being flown, and that's the point being made.

 

Thank you, Bob! I'm sorry I lost the rest of you in the rate of descent argument, but this is exactly what I was getting at the whole time.

 

So what do you guys think about the 15 degree versus 15 percent idea in my last post?... Do you think that's a plausable expaination?

[Guest pokey]

The rotorcraft flying handbook that you are referring to? is that AC61-13B? If so? does anyone (besides me)have the old one? AC61-13. My old one is dated 1965 & just for laughs i looked in there, the normal approach to a hover is 12 degrees in the old book 10 in the new. Steep is 12-20 degrees in old, 15 in the new. I would imagine that when they changed the numbers? they would have changed to % also, but? they are the FAA ! maybe the numbers will change to a more realistic value when 13C comes out.

anyhow, i agree --too steep for normal

[C of G]

Collective Down,

 

I'd be interested to see what math you are using to calculate the ROD required. It's been a while but I can't figure out how to come up with the equation for the distance and subsequent time required to get from the gate to the hover, to include the decel from 60 to 0. Thanks. Something I was always hoping to get an approach photographed from the side sort of time lapsed. Incidentally, I live in central Florida, so if you're serious about providing the helicopter................

[flyby_heli]

I would also be interested in the math. As far as i can figure, the rate of descent can only be calculated based on your groundspeed on the approaches, which is not really needed/useful information unless you are "flying the GPS" (or you would have to recalculate it before every approach with known/forecasted wind conditions). Throw in the deceleration from entry to a hover and also considering diminishing wind as you get closer to the ground due to surface friction and whatnot, and you got yourself one hell of a formula....you would spend more time calculating than aviating!!! We are pilots people, not mathematicians!!

On a calm day you would have to have a higher rate of descent to hit your spot at a given airspeed than you would on a day with say a 20 kt headwind, because your groundspeed is higher so you would get closer to your spot quicker.

 

This is probably the reason most of us fly angles of descent/rate of closure instead of airspeed or groundspeed/rate of descent approaches.

 

Flyby

[Superman]

Once again, fly over the threshold at 176 feet AGL (a 10 degree "normal" approach) or at 268 feet AGL (a 15 degree "steep" approach) and maintain a constant angle to the 1000 foot markers. Do this in any type at any approach speed that suits you, and let us know your impressions.

 

Well, I don't know about all the math you are doing, but I went and flew the approaches as you havelisted. crossing at 176 feet, 60 knots slowing and descending to the 1000' markers

[Guest pokey]

Well, I don't know about all the math you are doing, but I went and flew the approaches as you havelisted. crossing at 176 feet, 60 knots slowing and descending to the 1000' markers

 

 

yes, but? Superman? yer 'spossed to fly the approach in a helicopter, not yer blue & red suit !

[West Coaster]

What the hell is a runway threshold?