Approach Speed in GA Aircraft

[tcasblue]

I thought I might transfer some information from a post in another forum(with a few modifications for clarity)......If the aircraft is lighter than gross weight, the actual Vso is much lower than the book figure. In that case, on very short final, I will be bleeding off airspeed as I start to round out, and if I’m alone or with only one other person in a typical 4 or 6 passenger GA single, our airspeed should be significantly lower than the published 1.3 Vso.

If an angle of attack instrument is installed and used, which in effect compensates for weights lower than gross, the approach airspeed, both on long final and on short final, will be lower than book figures, sometimes dramatically so, especially in airplanes with a large W&B envelope. That’s because Vso is much lower.

I found the underlined part interesting. Do you agree with what was said?

[The Bullwinkle]

Sounds logical enough to me.

[BeechcraftPilot]

Very nice topic. I'd like to talk about light twins in this situation. We should consider speeds like Vmca during all phases, including approach and landing. Don't you guys think that can be a dangerous approach with less speed than published?

[john_tullamarine]

If the aircraft is lighter than gross weight, the actual Vso is much lower than the book figure. In that case, on very short final, I will be bleeding off airspeed as I start to round out, and if I’m alone or with only one other person in a typical 4 or 6 passenger GA single, our airspeed should be significantly lower than the published 1.3 Vso.

Some thoughts.

(a) stall speed ratio will vary near enough with the square root of gross weight ratio

(b) before playing with numbers, make sure you are working with CAS rather than IAS to avoid any problems with near stall PEC variation which can present a problem on occasion.

(c) I wouldn't necessarily use terms such as "significantly" lower - just do the sums.

(d) be wary of power (thrust) effects when comparing what you might be playing with in the aircraft with what the AFM/POH might have to say. The certification flight test requirements are fairly specific and thrust can play a significant role with the numbers

(e) Vso doesn't vary as it is a specific certification thing.

If an angle of attack instrument is installed and used, which in effect compensates for weights lower than gross, the approach airspeed, both on long final and on short final, will be lower than book figures, sometimes dramatically so, especially in airplanes with a large W&B envelope. That’s because Vso is much lower.

And ..

(a) keep in mind that you may be playing with varying the design rule book for your jurisdiction should you intentionally come aboard at speeds lower than what the AFM/POH suggests. Potentially, that could present a legal concern in the event of a mishap.

(b) I presume that the envelope reference is to CG range ? I can't immediately think of any reason why the GW range might have a material effect. For the CG range, the AFM/POH stall figures (and the usual operational figures based on the stall data) will be for forward CG as the stall speed varies somewhat with CG, due to tailplane forces coming in to play. Vso, however, is a certification animal and doesn't vary with CG, while the real world figures you might see on any given day may well show a measurable variation. Again, do be circumspect about playing outside the AFM/POH ambit due to the potential for legal censure in the event of a mishap.

[Pilot DAR]

Yes, the C of G position will affect the stall speed a small amount, Some flight manuals do present this data. That said, for the one or two knot difference, it's a nice target for approach speed precision, but rarely do I see a GA plane flown to within one knot of the target airspeed on approach. If you can, certainly do!

As my colleague mentioned, unless otherwise specified, stall speeds will be presented in calibrated airspeed, rather than indicated. Some flight manuals offer the courtesy of presenting it in both. Otherwise, this is a common error, a pilot believing that a stall is immanent based upon knowing Vso, but not as a CAS value, and watching the airspeed indicator to see it.

If you're using an after-market AoA system for very precise approach speeds, okay, but there are a few things to be certain of before you believe it 100%. You must determine if it was set up correctly. Two important factors really affect this: Does the plane have any modifications which affect lift (Gross weight increase, STOL kit, VG's, Wing extensions, for example)? If the plane does, the stall speed has probably been affected, and further, the relationship between IAS and CAS may be different, or, if the plane stalls more slowly, there will be a need to have IAS to CAS conversion for the slower speeds, which may not have been provided. This is extra important if there are multiple "lift" modifications, as the resulting stall speed will be a combination of the effects of the mods, and it will be very unlikely that there's an applicable IAS to CAS correction table. And, when the set up was done with reference to the airspeed indicator, was it recently calibrated? Kinda pointless if it was out!

Then, once you have determined the configuration of the plane (in terms of mods), and the availability (or not) of IAS to CAS correction for that exact configuration, you need to verify that the AoA was set up correctly. I have set up a few planes with an after-market AoA, and it was not trouble free. The manufacturer's instructions were unclear about the use of IAS vs CAS for the set up procedure. When I chose to make the required calculations based upon CAS, it was not possible, as each of the planes had wing mods, so the stall speed was slower, and there were no POH, nor flight manual supplement IAS to CAS correction tables for those slower speeds. So I set the planes up to the POH values, as it was all I legally could use, but it made the AoA system [conservatively] not as accurate as it could be. And, even the AoA system manufacturer states that the system may not be used for primary speed reference, in place of the original stall warning, nor for increased capability (slow approaches, shorter landings) - so it's really for entertainment only once you turn final.

My best (and very experienced) advice is to use the values in the POH, and expect the performance stated there. If the plane has mods, look for flight manual supplements. If there are multiple mods, and no one flight manual supplement provides information for that combination, you have been left with inadequate data to fly the plane (don't worry, you're not the first). When I approve airplanes (by STC) with combinations of mods, I do the testing and provide the flight manual supplement to support exactly that configuration.

A last word of wisdom, if you're flying a plane with wing mods which reduce the stall speed, continue to fly Vy climbs, and approaches at the POH speeds, to prevent being too slow in the event of an engine failure. Even if you're flying a glide approach, the fact that the wing has been modified to give you more lift (or you're seeing that on an AoA) will not give you any more reserve of energy in the flare. Roberston STOL Cessnas are famous (and the Roberston FMS warns) for pilots getting too slow on final, and not having enough reserve of energy to flare. If you're between 500 feet AGL, and he flare, you are most safe at either VY or "best glide" speed, at the slowest.

[ChickenHouse]

I thought I might transfer some information from a post in another forum(with a few modifications for clarity)......If the aircraft is lighter than gross weight, the actual Vso is much lower than the book figure. In that case, on very short final, I will be bleeding off airspeed as I start to round out, and if I’m alone or with only one other person in a typical 4 or 6 passenger GA single, our airspeed should be significantly lower than the published 1.3 Vso.

If an angle of attack instrument is installed and used, which in effect compensates for weights lower than gross, the approach airspeed, both on long final and on short final, will be lower than book figures, sometimes dramatically so, especially in airplanes with a large W&B envelope. That’s because Vso is much lower.

I found the underlined part interesting. Do you agree with what was said?
The question is: does it matter?

I.e. almost any landing I see in the US is far from slow or anything near Vso. I'd estimate they fly approaches 5 to 10 knots faster compared to the continent. Leaves us here. Who ever comes close to Vso in landings? Even the Cessna does honk far before any Vso and most pilots stay right at the edge of the horn even at short fields - not making use of the knots below horn and above Vso. I guess we all learned to fly on buttery controls in flight school, but suspect almost nobody goes slow flight afterwards. So back to my first question, the way we fly, where does it matter even though the physics may be correct?

[Archer4]

The question is: does it matter?


I agree with you. And for a second reason.
When flying slow the effect of turbulence on AoA will be higher. To compensate for this the safety margin needs to be higher. The end result is almost no benefit of the lower mass.
From a practical point of view the speed in the POH will take all these effects into account. Best not to overthink it.

[Jan Olieslagers]

The question is: does it matter?
I too concur. If you're too slow on approach, you feel it in your pants, right? If you are dependent on those precious instruments, what're you going to do the day they fail? This is what we train for - and take a refresher with an instructor, from time to time.

[oggers]

As my colleague mentioned, unless otherwise specified, stall speeds will be presented in calibrated airpseed, rather than indicated. Some flight manuals offer the courtesy of presenting it in both. Otherwise, this is a common error, a pilot believing that a stall is immanent based upon knowing Vso, but not as a CAS value, and watching the airpseed indicator to see it.

If anything it is the other way round. The IAS must be specified. You might see CAS or simply 'airpseed' in preamble such as specifications but in the part of the AFM where it counts the airspeeds must be indcated airspeed (even though one may see CAS alongside). I refer below to CS 23 as it appears to be identical to the old Part 23.CS 23.1545 Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds...
...a white arc with the lower limit at VS0 at the maximum weight,

CS 23.1581
(c) The units used in the Airplane Flight Manual must be the same as those marked on the appropriate instruments and placards.
(d) All Airplane Flight Manual operational airspeeds, unless otherwise specified, must be presented as indicated airspeeds.



https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/528x496/c172_pa28_afm_white_arc_325e771487704175f578d409a63eeaa02b47 4693.png

[oggers]

I too concur. If you're too slow on approach, you feel it in your pants, right? If you are dependent on those precious instruments, what're you going to do the day they fail? This is what we train for - and take a refresher with an instructor, from time to time.

Well it does matter when you are flying commercially into short strips. The stopping performance is predicated on the correct approach speed for the weight. If you fly any faster you are inviting an overshoot. Flying the correct airspeed becomes very important. Should the ASI fail you fly powers and attitudes and take it somewhere with a healthy stopping margin.

[Pilot DAR]

The IAS must be specified. You might see CAS or simply 'airpseed' in preamble such as specifications but in the part of the AFM where it counts the airspeeds must be indicated airspeed

The design requirement states that Vso is defined in CAS

Sec. 23.49

Stalling speed.

(a) https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/c67ae5aeda8f8f5185256687006b8f49/SectionRule/0.24A!OpenElement&FieldElemFormat=gifis the stalling speed, if obtainable, or the minimum steady speed, in miles per hours (CAS), at which the airplane is controllable,................

Therefore, if a pilot is factoring stall speed, the speed being factored should be the CAS speed, and the factor should also be CAS. So, if you want to fly a 1.3Vso approach, a pilot would have to know Vso in IAS. Perhaps the flight manual conveniently provides this. If not, the pilot will have to find it them self by observing IAS at the point of the stall, correcting to CAS with the flight manual table, multiplying by the factor in CAS, obtaining the result, and correcting back to IAS for reference to the airspeed indicator reading. For some types, there can be a 10 knot difference between IAS and CAS at the stall.

I agree that that the use of IAS and CAS can be inconsistent among manufacturer's and types, particularly in the earlier years. And, it would appear that values required to be presented in CAS are being marked on the airspeed indicator in IAS. Once random example of this would be for a 1974, Cessna 185; the POH Airspeed correction table (table 6-1) states "Maximum flap speed 110 MPH, CAS", though in the line above states flaps down IAS is 110, where the CAS is 112. So one would infer that the white line should begin at about 108 MPH to assure that the flaps speed limit is actually observed in CAS. But, on page 4-2, Airspeed limitations, which does state the limits are in CAS, states that the white arc (which is what the in indicating (IAS) pointer shows) is 110 MPH.

Now the 2 MPH difference is not going to create a risk to safety of slight, but it serves to demonstrate the the interchanging of IAS and CAS, even in a POH has been done such that a pilot should really pay attention.

I agree with Chickenhouse that approaches tend to be flown fast, and too fast, more often that at 1.3Vso. Note that 1.3 Vso is a minimum speed for certification (23.73), the manufacturer may recommend a faster speed. Again referring to the 1974 C 185 (just 'cause I have the book open), full flap stall speed is 56 MPH CAS, X 1.3 = 73 MPH CAS = 69 MPH IAS, so to fly a full flap 1.3 Vso approach, the math would have you at 69 MPH IAS. The POH (page 2-20) says: "For short field landings, make a power off approach at 78 MPH with 40 flaps....". This corresponds to page 1-7, which states landing airspeed of 75 - 85 MPH flaps extended. We have to presume that the POH is presenting these speeds as IAS, though it does not state. Now if that plane has a Horton STOL cuff on the wing, all those speeds will be different, and there is no flight manual supplement to tell the pilot the different speeds (or even a placard saying that they might be different)!

[Jan Olieslagers]

Well it does matter when you are flying commercially into short strips.
You did observe that we are discussing "private flying", here? Not that I am unwilling to learn from the professionals, though.

agree with Chickhouse
I love it! - sorry @DAR, that was irresistible.

[Fl1ingfrog]

To follow on from oggers we are in the danger of fiddling with detail but with little gain. I'm not a fan of the various AofA gizmos either and to be frank I find them a bloody irritating distraction. The fans of these things become infatuated by them. Power plus attitude is equally of value whether during the climb out or on the approach just as much as it is in the cruise. If you are too slow the controls will be sloppy - take heed. Adding airspeed arbitrarily should be avoided always because at some point you will need to land. Using the formal standard 1.3 the stall is already a safe speed to use for a particular weight but controllability is also important and using the POH approach figures, which will normally be well above that, is more than enough. There can be no case for adding to the POH speeds for turbulence, this suggestion is wrong and foolish in my view.

Using the 1978 172N POH figures, the Performance Specifications figures give the stall: zero flaps 50kts CAS and with 40 degrees of flap 44 kts CAS. At these speeds the IAS is 9 kts higher according to the airspeed calibration table. However between 60 - 90 kts the CAS/IAS is mostly the same or varying to a maximum of just 2 kts. In line with most light aircraft the variation in CAS/IAS for approach speeds is inconsequential.

The Cessna 172N recommended approach speeds are: flaps up 60-70 KIAS, 40 degrees flap 55-65 KIAS. For Short field they recommend 60 KIAS. At these speeds the CAS and IAS are the same both on the approach and of course the climbout. It is worth noting, as its been mentioned, that the stall speed can vary by 5 KIAS between the most forward CG and the most rearward CG permitted for this aeroplane.

[Pilot DAR]

agree with Chickhouse
I love it! - sorry @DAR, that was irresistible.

Pardon me! Typo corrected!

[KayPam]

(a) keep in mind that you may be playing with varying the design rule book for your jurisdiction should you intentionally come aboard at speeds lower than what the AFM/POH suggests. Potentially, that could present a legal concern in the event of a mishap.

Some manuals will take into account different approach speeds for different weights. For example the TB20 gives you performances with two different weights leading to two different speeds.

Another problem I would like to point out on this topic is that some light aircraft operators tend to recommend speeds higher than 1.3Vs and higher than the manual.
If the manual tells you to approach at 1.4Vs, for example, then OK. But if the manuals recommends 1.3 and your airclub 1.6, what then ?
This will lead to a habit of very long flares.

[oggers]

The design requirement states that Vso is defined in CAS

Yes I have seen that reg. Design airspeeds are CAS but operational airpseeds are IAS. The information has to be made available to the pilot in IAS as stated in the regulation 23.1581 that I quoted. Instrumentation during the flight test will determine the CAS, but the production airspeed system is also used in order to determine the IAS, which is what the pilot needs to know.

Therefore, if a pilot is factoring stall speed, the speed being factored should be the CAS speed, and the factor should also be CAS

Yes I agree. If you wish to factor the stalll speed the process is [CAS x factor] and then convert to IAS using the airspeed corrections table. No argument. The point I was responding to was:
stall speeds will be presented in calibrated airpseed, rather than indicated. Some flight manuals offer the courtesy of presenting it in both
...this is not a courtesy. The requirement for operational airpseeds in the AFM is 'indicated':(c) The units used in the Airplane Flight Manual must be the same as those marked on the appropriate instruments and placards.
(d) All Airplane Flight Manual operational airspeeds, unless otherwise specified, must be presented as indicated airspeeds.

[Vessbot]

I agree that that the use of IAS and CAS can be inconsistent among manufacturer's and types, particularly in the earlier years.

I remember the Aeronca Champ having a placard that listed some speeds as "true indicated airspeed" - go figure!:sad:

[Pilot DAR]

The requirement for operational airpseeds in the AFM is 'indicated':
(c) The units used in the Airplane Flight Manual must be the same as those marked on the appropriate instruments and placards.
(d) All Airplane Flight Manual operational airspeeds, unless otherwise specified, must be presented as indicated airspeeds.


Yes, I agree, noting that this requirement is for a latest FAR Par 23 certified plane, but is not a requirement for a CAR 3 or older 23.1581. CAR 3.777 makes no mention of IAS/CAS. CAR 3.778(a) also makes no mention, though points you to 3.757, which refers to TAS (just add to the confusion, I suppose!). 23.1581 does not seem to mention IAS until revision 23-50 of 1996. So any plane certified prior to that would not have to comply.

So the complication comes in a later manufactured CAR 3 plane (like a 172/182/206) where the requirement in the certification basis (CAR 3, and earlier 23.1581), did not specify presentation in IAS/CAS, so it's not required, but Cessna presents it anyway, as they would be required to for a latest 23-1581 cert basis plane. Using the C 206H as an example, its a FAR 23, amendment 6 cert basis plane, so it's not required to comply with 23.1581 at amendment 50, but Cessna can voluntarily do so, and it's wise. I find that generally, Cessna go the extra distance for POH information (probably at the legal team's advice!)

These details are well beyond what we would expect the pilot to be aware of, and it's probably annoyingly confusing to most pilots. But, as the planes and certification basis have evolved, and flight manuals/POHs have been refined, pilots need to be reminded to read and interpret what's presented in the POH in context. IAS/CAS awareness is important if you're actually using an airspeed indicator during flight near the stall speed. It's extra important if you're setting up and AoA system, and then has an additional layer of complexity for each lift mod installed on the plane.

[oggers]

Yes, I agree, noting that this requirement is for a latest FAR Par 23 certified plane, but is not a requirement for a CAR 3 or older 23.1581. CAR 3.777 makes no mention of IAS/CAS. CAR 3.778(a) also makes no mention, though points you to 3.757, which refers to TAS (just add to the confusion, I suppose!). 23.1581 does not seem to mention IAS until revision 23-50 of 1996. So any plane certified prior to that would not have to comply

Your ability to track down the various iterations of the regs is impressive. Incidentally, those extracts from POHs I pasted above are both from the '70s. As regs do change over time, the general advice, as ever, has to be 'consult your AFM'.

[Fl1ingfrog]

If the manual tells you to approach at 1.4Vs, for example, then OK. But if the manuals recommends 1.3 and your airclub 1.6, what then ?

Simple, you fly the aeroplane in accordance with the POH/AFM. No one including flying/schools/clubs or any other "operator" have the right to demand anything different. When differences are demanded they are usually based on ignorance, hearsay and the thoughtless but well honed " that's what we've always done here".

[selfin]

Well it does matter when you are flying commercially into short strips.

The Canadian CPL test requires candidates to calculate the stall speed in the landing configuration for the predicted landing mass.
Ex 2B in the Canadian Flight Test Guide: https://tc.canada.ca/en/aviation/publications/flight-test-guide-commercial-pilot-licence-aeroplane-tp-13462#ex2b

[Jan Olieslagers]

But again, that is about a CPL, not about "private flying".

[Pilot DAR]

Your ability to track down the various iterations of the regs is impressive.

Thanks, my role as acting on behalf of Transport Canada to issue STC approval for modification requires me to be up on these small details. Some modification approval projects can be horribly cost burdened by having to show compliance to a more recent amendment of the design requirement or not. The determination process (for every STC project), known as Changed Product Rule decision, focuses on exactly which amendment of a particular design requirement will be applied. It can be item by item, as it was when I participated in the re-engine of the DA-42 to Lycoming. This is the "certification basis" for the STC. It's usually the same as that for the original type certificate, but not always. There are times where either the Engineers at TC, or I will propose to show compliance to a more recent amendment of a design requirement during certification, when doing so will result in noticeably improved safety.

I've done a fair amount of position error correction flying. I have a program coming up in a week or so on a AS350 helicopter with a previously approved external assembly, which is suspected of inducing a PEC error (static port partly obscured by the mod). My work to approve a new pitot tube and static port arrangement on the DC-3T's in Germany has been put off until next year. That will involve a lot of flying, and some fiddling with static ports to get within the required limits of error (it has too much right now to be approved, so the original system is still in use).

Interestingly, while I was test flying an older Cessna 210 last week, following a massive repair I had to approve, I noticed that the operation of the landing gear momentarily affected the static ports, and induced a bounce in the altimeter and VSI. After landing I had a look and noticed that Cessna had placed the static ports up and behind the main gear doors. Obviously, with the main gear doors open, there is a static disturbance. But, the doors close again after the gear extends, so it's not really a problem, as long as you're aware.

If the manual tells you to approach at 1.4Vs, for example, then OK. But if the manuals recommends 1.3 and your airclub 1.6, what then ?
Simple, you fly the aeroplane in accordance with the POH/AFM. No one including flying/schools/clubs or any other "operator" have the right to demand anything different.

Agreed. If the flying club/school.operator would like to have the airplane operated noticeably differently to what the flight manual/POH says, they should apply for an STC, with which they will get an approved Flight Manual Supplement for the operation they desire - if it's worthy of approval. A needlessly fast approach, if ever to be approved, would be accompanied with changed procedures, and performance data. Fly it the way the original flight manual/POH and any supplements describe.

[Fl1ingfrog]

Jan - It is of no consequence whether the aircraft is flown by a commercial pilot for commercial operations or flown by a private pilot for private purposes: It is still the same aircraft and therefore it flies the same.

For the CPL skill test and throughout the training the operation of the aeroplane must be strictly in accordance with the aircrafts POH. Whether flown by a CPL or a PPL it is the deviations from the correct ops that lead to accidents.

[3wheels]

Average SEP 65/70 knots ...end of.

[Forfoxake]

Average SEP 65/70 knots ...end of.
If I approach at this speed in my SEP, I will usually go through the far hedge unless I have the good sense to go around and try again at the correct approach speed for my aircraft (around 50 knots).

[Pilot DAR]

Average SEP 65/70 knots ...end of

Yeah, I suppose that would be a fair average of the different SEP types I fly. However, there are only a couple I would actually approach at that speed, others would be faster, or slower, in accordance with the POH recommended speed.

[V1... Ooops]

I'd like to talk about light twins in this situation. We should consider speeds like Vmca during all phases, including approach and landing. Don't you guys think that can be a dangerous approach with less speed than published?
Vmca is not a concern during the final phase of approach and landing, once one has committed to land. The Vmca published for a light twin (FAR 23 twin) is based on one engine at takeoff power and the other one inoperative. During the final phase of approach and landing in a typical light twin, each engine is only producing about 25 to 30% of rated power. Should one fail, the other only needs to be increased to 50 to 60% of rated power.

In real world operations, if you are 5 mile back on the ILS, you are almost always above Vmca, so it's not a concern. At one mile from the threshold, when you start slowing down to Vref, you are generally committed to landing, hence there is no possibility that you would need to apply 100% power to the operative engine in the event of an engine failure.

My comments are based on thousands of hours in a 12,500 pound twin turboprop, but I think the same concepts would apply to most light twin engine aircraft.

[V1... Ooops]

Yes, I agree, noting that this requirement is for a latest FAR Par 23 certified plane, but is not a requirement for a CAR 3 or older 23.1581. CAR 3.777 makes no mention of IAS/CAS. CAR 3.778(a) also makes no mention, though points you to 3.757, which refers to TAS (just add to the confusion, I suppose!). 23.1581 does not seem to mention IAS until revision 23-50 of 1996. So any plane certified prior to that would not have to comply.
PilotDAR is correct. When I rewrote the AFM for the Series 300 Twin Otter in 2012, I converted and published all the airspeeds in IAS. Because that aircraft was originally certified as a CAR 3 aircraft, AFM speeds had been given in CAS since original certification in the 1960s. So, in this particular case, it was a 'courtesy' (common sense is what I would call it) to publish the speeds in IAS - legally, I could have continued to use the original CAS speeds.

[BeechcraftPilot]

Thanks for the answer! I fly a Baron 58 and your comment describes exactly what we do. Since the main purpose of this topic is to talk about speed management regarding weight, the first thing that I was thinking was about Vmca.

We always follow the speed published by the manufacturer, the difference is the % of power we use to maintain the approach speed. Basically, the approach speed will be the same, with less or more weight. - Talking about light twins.

As an example, Flight Safety recommends flying base leg with 110 KIAS (Baron G58, visual approach). The Vref is 95 KIAS and Vmca 84 KIAS. The MTOW is 5,500 lbs.

[Maoraigh1]

"Average SEP 65/70 knots ...end of.
If I approach at this speed in my SEP, I will usually go through the far hedge unless I have the good sense to go around and try again at the correct approach speed for my aircraft (around 50 knots.)"
​​​​​​Can the approach speed in a low-inertia aircraft be too high, provided the "at threshold" speed is achieved? It can be too low.

[Fl1ingfrog]

Well Mouraigh1, as the saying goes "it's only the last nanometer that matters" but, this is much too easy to say. Most accidents/incidents come about because of an unforeseen event culminating in a distraction and pilot overload. Sod's law tells us that Sod is always around just waiting for his moment to strike. For the most part poorly applied approaches more often than not do not lead to an accident but that is usually down to fortune: i.e. Sod being pre-occupied elsewhere. If you follow 'Murphy's law Sod won't always be elsewhere. I suggest you take a look at James Reason's 'Swiss Cheese Model'. It is worth a google.

A stable well flown approach will always maximise the cognitive reserve to enable the pilots to deal with the unexpected and thus avoid the slips and errors which are always a major ingredient of accidents.

[fitliker]

The POH /AFM are usually the best source for numbers .
The difference between IAS ,CAS and TAS in GA are so small that it is really and truly Academic.

A-Question may arise as to “when “you might choose to use a speed other than flight tested and approved by the sky gods .
Gusty conditions and Cross winds you might want to add some airspeed to give a little bit more control .
Aircraft might be damaged and it starts to do weird stuff when you slow down . I had the top corner of a windscreen depart in a spin . The slowest speed I could get and still have pitch control was 90 KIAS , so I landed at 90 . I was surprised how quickly it stopped on the ground . I was expecting to go off the end . But the drag from the big hole slowed the plane in under 2000 feet .
Changes were made to a few aircraft window seals after that flight .

General rule is you never want to be slower than the POH recommended speeds .I flew with a guy who used really slow speeds for short fields , but you would never deliberately land somewhere that was so short you could not get out again . Almost a helicopter approach . I Showed him how to land a 172 in 150 of ground . It was fun but the slightest turbulence and it would have got expensive real quick . Pointless exercise as you need at least three times that to get into ground effect for departure in a light plane into wind .

Many students get the airspeed covered in the circuit to prove that the airplane can be flown without the airspeed indicator working , you just have to give yourself more room and do not rush the approach .

Time to Fly

[Pilot DAR]

The difference between IAS ,CAS and TAS in GA are so small that it is really and truly Academic.

The difference between IAS and CAS at the approach or stall speed in some GA types can be as much as 9 knots. That's not "small", and worth consideration.

[fitliker]

I try to keep it simple when training other pilots . I just use KIAS when I am sat in the aircraft .
I am not trying to dumb it down too much just not trying to reduce workload and keep it simple .
At the end of the day the indicated airspeed is the easiest number to use . Most of the trainers I have flown the differences was usually less than the thickness of the airspeed indicator needle above 60 kias.
Although it is possible to land a Cessna 152 with no airspeed indicated , fun demo for other instructors , I have rarely demonstrated students that because once they are in ground effect the dials can be a distraction and at that point it is better to pay attention to flying the aircraft .

Time to Fly

[Pilot DAR]

Most of the trainers I have flown the differences was usually less than the thickness of the airspeed indicator needle above 60 kias.

Yes, that's my experience too, though the IAS/CAS error increases to as much as 6KIAS below 60 for the 152, a big needle width. I agree that the student will not be flying to that, but they should be conversant with it. The IAS/CAS difference should not be dismissed. On other types (some C 206) it can be as much as 14 MIAS at the stall, and the pilot should be aware of the importance of the difference. This is particularly true of Cessnas with STOL kits installed, which are common for privately owned ones, and not common for flying schools. Instructors should assure that pilots who may transition without additional familiarization training are aware of this factor....

[fitliker]

When I was checking new Mooney pilots for insurance checks , the difference between normal cruise and Va was interesting .
The Piper Meriden had quite a difference between normal cruise and Va . Both popular private aircraft .
Both aircraft had over forty knots to lose if you got into rough air or it could make life uncomfortable in the Mooney , in the early Piper Meriden the wings would fold . The FAA issued an Ad and got it fixed .
Most Aircraft get uncomfortable above Va in rough air and I only recommend flying above Va or Vb if you like to scare yourself , scare your passengers or you enjoy cleaning vomit out of airplane ceilings and carpets . Or like wrinkles in your aircraft skin to match your wrinkles ?
I am always close to Va if I am near Strato fractus ,big winds or near mountains , just a personal preference . People never remember the extra minutes the flight takes , but they will remember the scarey bumps if you do not respect Va .
The old Cessna airspeed indicators used to have a yellow arc . Top of the arc if you were heavy , bottom of the arc if you were light made Va simple .
i do not understand why they stopped painting the yellow arc on the airspeed indicators . How expensive is yellow paint ?

[Archer4]

The old Cessna airspeed indicators used to have a yellow arc . Top of the arc if you were heavy , bottom of the arc if you were light made Va simple .
i do not understand why they stopped painting the yellow arc on the airspeed indicators . How expensive is yellow paint ?

Be careful with any conclusions. It might be on purpose. For example there is a difference in the white arc area. For some engines on the Cessna's the white arc goes all the way down to 0. For some it doesn't. This is related to the mandatory or optional use of the carburator heating for lycoming engines. Something similar might apply to the yellow arc (no idea what though).

[oggers]

The old Cessna airspeed indicators used to have a yellow arc . Top of the arc if you were heavy , bottom of the arc if you were light made Va simple...i do not understand why they stopped painting the yellow arc on the airspeed indicators . How expensive is yellow paint ?

'They' have not stopped. The top of the yellow arc is Vne (aka upper redline speed). The bottom of the yellow arc is Vno. Va is different to bottom of the yellow arc. The coloured arcs have been standardised and required by the regulations since 1945.

[Pilot DAR]

The old Cessna airspeed indicators used to have a yellow arc . Top of the arc if you were heavy , bottom of the arc if you were light made Va simple .
i do not understand why they stopped painting the yellow arc on the airspeed indicators .

The yellow arc on some airspeed indicators is not necessarily related to Va. Va will generally be slower than the bottom of the yellow arc. Va is the maximum speed at which the pilot could overstress the plane with large pitch control inputs. Slower than that speed, a large control input would result in a stall, which would automatically unload the stress on the wings. Va is not normally marked on the airspeed indicator, but rather placarded, as it varies by weight.

The beginning of yellow arc on the airspeed indicator is the maximum structural cruising speed (Vno). Faster than that speed, a prescribed gust (by design standard) could overstress the plane without pilot input. Hence the limitation that flight at speeds in the yellow arc be conducted with caution in smooth air only (meaning avoid turbulent air, and don't handle the controls roughly).

The top of the yellow arc is Vne, it is certain that at Vne, you are well above Va at any weight, so you should already be being very gentle on the controls.

For some engines on the Cessna's the white arc goes all the way down to 0. For some it doesn't.

I'm not aware of a white arc on any engine instruments. The white arc on the airspeed indicator is the flap speed limitations, and will extend from full flaps stall speed (IAS usually) to the maximum full flaps extended limiting speed. There may be a green arc on the tachometer, which on most shows the normal operating range for the engine (cruise data provided), though I agree that I have seen some tachometers which at marked green from the maximim RPM (red line) back to zero RPM, I don't know the logic of this. A few Lycoming powered plane with certain props also have a yellow arc within the greed arc, nothing to do with airspeed, it's a propeller vibration caution.

[Forfoxake]

"Average SEP 65/70 knots ...end of.
If I approach at this speed in my SEP, I will usually go through the far hedge unless I have the good sense to go around and try again at the correct approach speed for my aircraft (around 50 knots.)"
​​​​​​Can the approach speed in a low-inertia aircraft be too high, provided the "at threshold" speed is achieved? It can be too low.

OK, Maoraigh1, I know I can approach a bit faster and usually slow it down in the last couple of hundred feet (and will do so if it is very gusty). However, I find that a stable approach of 50 knots on finals (in a Kitfox 5, which, like all Kitfoxes, is slippier than it looks) usually leads to a better landing probably for the reasons outlined by Fl1ingfrog.

So yes, the approach speed in a low-inertia aircraft can certainly be too high!

[Jan Olieslagers]

a Kitfox 5, which, like all Kitfoxes, is slippier than it looks
Flying a Kitfox derivative, but not being a native English speaker, I find this phrase fascinating and a bit bewildering.
How do you define or describe a "slippy" aircraft?
What is the relation between a plane's appearance and its "slippiness"?

[Forfoxake]

Flying a Kitfox derivative, but not being a native English speaker, I find this phrase fascinating and a bit bewildering.
How do you define or describe a "slippy" aircraft?
What is the relation between a plane's appearance and its "slippiness"?

Sorry to have confused you. Maybe I should have said more slippery or less draggy!

However, imho slippy looking aircraft tend to have short, smooth and thin wings, small and/or very closely spatted wheels, fairings where two surfaces meet and all gaps sealed as much as possible.

They do not tend to have long, thick, fabric-covered wings, very large wheels and tyres, struts, not many fairings and large gaps at the front of the control surfaces. These features are typical of the Avid Flyer and it's derivatives.

Nevertheless, what I was trying to convey was that they will float a long way on rounding out if you approach 10-15 knots too fast.

[Jan Olieslagers]

Ok, thanks, and no need to apologise! I have always thought my Apollo Fox a very nice compromise on all those factors, certainly for the beginner pilot that I consider myself. And yes, I found I can land on 200 metre runways, but then I must be really sharp on the approach speed.
Witness my first and only crash, luckily to very limited harm, when I was too high and one second later too fast when landing at Liernu EBLN - and one second late in realising I'd been better to go around.

[Maoraigh1]

ASI top left is in knots
ASI​​https://youtu.be/06Clghh329g

[Bosi72]

I assume the topic poster, like like majority people around the world, is flying in at least 20 years old aircraft (I fly in 60 years old C172A).
Regardless, after so many years of use I wouldn't trust 100% what's written in the POH/AFM, neither I would trust gauges (although I always do sanity check by comparing with GS).
The only way to test the stall speed it is to climb above 3000ft, then slow down and note down when it stalls.
Still, no ground effect up in the sky, neither air density/pressure/temperature is the same, neither every day is the same, but the Vso value should be very close to what's in the books.
Regardless, my safety speed is Vso 35kts x 1.404 which is 49kts, but I normally approach with 60.
Unless STOL aircraft or an aircraft with STOL modifications, I wouldn't be experimenting too much :)
Safe landings !

[zzuf]

The yellow arc on some airspeed indicators is not necessarily related to Va. Va will generally be slower than the bottom of the yellow arc. Va is the maximum speed at which the pilot could overstress the plane with large pitch control inputs. Slower than that speed, a large control input would result in a stall, which would automatically unload the stress on the wings. .
Mmmm....
Va is a design speed, it does not vary with weight. The only time Va has any relationship to stalling in FAR 23 is if Va is chosen to be Va min.
I am aware of many aircraft manuals giving Va for weight. FAR 23 is clear, Va is determined at the design weight. These operating manual "Va's" are really more like VO, but I have no idea how they have been determined.

Below is a cut and paste of AC 23-19A which is very clear in the lack of relationship between Va, stall and structural strength - except in one particular circumstance, that if the designer decides to us Va=Va min

"48. What is the design maneuvering speed VA?

a. The design maneuvering speed is a value chosen by the applicant. It may not
be less than Vs√ n and need not be greater than Vc, but it could be greater if the applicant chose the higher value. The loads resulting from full control surface deflections at VA are used to design the empennage and ailerons in part 23, §§ 23.423, 23.441, and 23.455.

b. VA should not be interpreted as a speed that would permit the pilot
unrestricted flight-control movement without exceeding airplane structural limits, nor
should it be interpreted as a gust penetration speed. Only if VA = Vs √n will the airplane
stall in a nose-up pitching maneuver at, or near, limit load factor. For airplanes where
VA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would
exceed the limit load factor.

c. Amendment 23-45 added the operating maneuvering speed, VO, in § 23.1507.
VO is established not greater than VS√n, and it is a speed where the airplane will stall in a nose-up pitching maneuver before exceeding the airplane structural limits."

[oggers]

Mmmm....
Va is a design speed, it does not vary with weight.

OK Va is the design manoeuvring speed but the operating manoeuvring speed does vary with weight which is important to understand. I have edited this because on reflection I think you explained it with the reference to the AC. Going through some AFMs I see this conflation of Va and Vo you mention so it is a good point you have raised.

[Forfoxake]

ASI top left is in knots
ASI​​https://youtu.be/06Clghh329g (https://youtu.be/06Clghh329g)

Impressive but I prefer a stable approach of around 50 knots at the 230-530m grass strips I typically fly my Kitfox from.

[jmmoric]

Piper 28-181 Archer II.

Approach speed 66 knots.
Stall speed fully loaded 53 knots.

I usually do the base at 76 and downwind at 86... don't know why... but someone taught me to add 10 knots from the final back in the day.

I would do less than the 66 when approaching a short runway.... we have winglets installed, and the damn aircraft tends to float..... a lot..... if you're a bit too fast.