View Full Version : how to determine "positive rate of climb "

6th Dec 2009, 00:17
From 737's FCTM:"Retract the landing gear after a positive rate of climb is indicated on the altimeter."
so the qiz is:"how to determine a positive rate of climb?" From altimeter? or VSI? :confused:
looking forward for your replies, thank u!

galaxy flyer
6th Dec 2009, 00:20
Or increasing radar altitude or visual indications (Earth getting smaller!). Traditionally, it has been TWO indications of climb, take your pick, 2 out of 4.


6th Dec 2009, 00:40
thank u,but that's a personal's experience.what i'm bothering with is how to write the words into an SOP.
BOEING has said"from altimiter", i think it's partly reasonable---VSI indication is from IRS. but how to read the positive rate of climb from an altimiter?
so far, the criterias for retracting gears in my mind are:
1.not too early---at least airborne,
2. not too late---too late will affect the performence(especially in case of 1 eng INOP)
any words from your company's SOP?

6th Dec 2009, 00:50
or any Boeing expert can explain this?

galaxy flyer
6th Dec 2009, 00:56
Sorry, not a Boeing expert. Our book just says "positive rate of climb".


6th Dec 2009, 01:01
From PanAmerican, long ago...

A positive rate of climb as indicated by a sustained increase of altitude as indicated by the pressure altimeter.

Rad Alt.. No.

Pressure altimeter...Yes.

6th Dec 2009, 01:02
VSI indication is from IRS

Usually the VSI indication is from the ADC's and corrected for a quicker response by the IRS or another accelerometer source.

I would not confine yourself to stating the observed indication if your aviation authority will buy off on "positive rate of climb" as is in galaxy flyer's book. It is easy to write a operation manual, much harder to change it later.

6th Dec 2009, 01:24
On B777 my company we use Altimeter/VSI, VSI is important because as mentioned above it is coming from IRS so it has No Maneuver Induced Errors :ok:

Bruce Waddington
6th Dec 2009, 01:51
Eagle 737,

The bunch I worked for used;

for the Airbus fleet... "retract the gear when the vertcal speed is postive and the radio altitude has increased"

for the B777 fleet... "retract the gear when a positive rate of climb (is) indicated on the altimeter and the RA."

On the Lear 45 I fly now the wording in our SOPs is retract the gear "at positive rate of climb on both the IVSI and the radar altimeter."

The actual wording differs between types but the intent is the same ... make sure you have two indications and then retract the gear.

best regards,

Bruce Waddington

sudden Winds
6th Dec 2009, 03:19
depends on the aircraft u fly, the 737 requires both an altimeter and VSI movement (upward;)) to call for +ROC.
Large a/c like the A340 uses radio altimeter info. The reason for this is that the static ports are located near the nose of the a/c and when u rotate, u can have an altitude increase and a VSI movement during rotation with the wheels still on the ground.

6th Dec 2009, 05:27
If you read it from the VSI, it is named: "positive rate of climb". (600 feet per minute, 1000 per minute, etc....)

If you read it from the altimeter, it is called: "positive climb".

6th Dec 2009, 06:25
Isn't a climb by very definition positive? A negative climb would be a descent would it not?:):)

6th Dec 2009, 07:16
Greetings, I think that the Altimeter alone is not enough, because maneuver induced error may still be hanging around :E

6th Dec 2009, 08:41
I look out the window.

6th Dec 2009, 09:03
how to determine "positive rate of climb "

Listen for the click as the landing gear lever solenoid unlocks? ;)

Using a VSI reading - on a significantly up-sloping runway you can get numbers appear before you've left the ground. The old Teheran airport comes to mind.

Radalt would seem to be more reliable as static sources can misbehave during rotation on some aircraft.

6th Dec 2009, 09:12
I don't think you can beat the rad alt on B747, it is calibrated to the level of the tyres. Also it has no errors induced by manoeuvring. You would, of course, be a mug not to ensure that you have at least 2 indications of increasing distance from mother Earth.

Mr Optimistic
6th Dec 2009, 10:12
Sorry to butt in but presumably there is an interlock to stop retraction if there is a load on the gear, ie oleo compression ?

6th Dec 2009, 10:53
There is, its called a squat switch. If its serviceable you have no worries but there have been many retractions on the ground.

6th Dec 2009, 11:22
Isn't a climb by very definition positive?
I think "positive" is used in the sense of "definite" rather than "greater than zero" in this case.

Why over-complicate things? There is no need to start writing a thousand words into your manual to define something which is not an operational problem - you end up with a wordy over-bloated manual, which (because of it's nit-picking definitions) is more susceptible to bush-lawyer interpretations rather than being simple and clear.

I can't think of a single accident, where the gear has been retracted so early on take-off that it resulted in a problem, so leave it at "positive rate of climb" and forget about it.

6th Dec 2009, 11:34
I'm not sure that relying on the RadAlt to show a +ROC is a good idea. I know a number of airfields where the ground slopes away at the end of the runway!

By George
6th Dec 2009, 12:13
'Mustafagander', I agree, the RAD ALT on the 747 always reads -8 feet on the ground. This is the length of the 'truck'. On landing, 'heel' first (unlike the 767 which is toe first) the RAD ALT indicates 'zero' and -8 feet once the whole lot is in contact. Very accurate. All this is abit technical, there are many obvious clues that one is going 'up', including the loud gear relay switches. I agree you need two sources and need to have it correct in the manual, but isn't it sad everything including the bleeding obvious has to be a SOP.

6th Dec 2009, 13:10
If you're not sure whether the a/c has a positive rate, or not.....

Perhaps you ought to give up flying and take up something less challenging. Knitting maybe.

I realise that they have to write a rule for everything these days (and for the record, where I work you are supposed to wait til the climb shows on the altimeter).

What happened to airmanship?

6th Dec 2009, 14:30
Hi eagle737,

There are lots of suggestions there and most point to having at least two sources indicate a climb.

In the simulator with an engine failure on take off, I've seen some excited crews call "+ve climb" when we are about 5 feet radio, and the aircraft is hardly climbing yet. The open gear doors create more drag initially, and some crews may fly level for a while or even sink a little.

So the "+ve climb" call needs to be made after being certain the aircraft is safely climbing away from the runway, and not just an automatic call having seen one instrument twitch. The day you have a real engine failure on take off is the one time you don't want to make that call too early.

6th Dec 2009, 14:39
Take into account runway slope. You can have positive ROC with the wheels still on the ground!

6th Dec 2009, 14:42
Or increasing radar altitude or visual indications (Earth getting smaller!).

I like the latter part. Might not work for the A343 though, too subtle...

Pugilistic Animus
6th Dec 2009, 19:16
when you lose sight of the muppets:}

6th Dec 2009, 22:36
I'm with BarbiesFriend. If you cant work out if the aircraft has left the ground then you need to find another job. It aint difficult!!!!!!

6th Dec 2009, 22:48
Blimey, how complicated do we want this to be? I'm with barbiesfriend and qwerty. When the big needle on that clock like altimeter thingy is moving clockwise and the VSI needle has got a slight upward pointy angle?

6th Dec 2009, 23:10
VSI indicating climb, altimeter increasing, radalt increasing and beyond 20'?

If you want ball park guidance, keeping it practical and it's not further clarified in SOPs and it's 125m visibility in complete overcast then how about that then?

7th Dec 2009, 04:04
The open gear doors create more drag initially

Very true for some light twins.

But the question was asked initially for the B737? In this case, there in no real gear doors. Even none on the main gear. Concerning the nose gear, they are already open when the gear is down.

7th Dec 2009, 10:08
Hi Kag,

I don't know what you operate, but most of my previous types have large doors which open to let the gear transit, then close around the extended gear. Hence 3 limiting speeds with the gear: 1) Extended, 2) Lowering, 3) Raising.

What's yours?

Hey Driver
7th Dec 2009, 10:12

The 737 FCTM used to read “positive rate on the IVSI and Altimeter”

I believe that due to the sensitivity of the Instantaneous VSI this requirement was removed.
Using only the Altimeter, with its pressure lag, is a more conservative indication of positive rate. Particularly in a windshear encounter.
In a two crew aircraft both pilots are confirming positive rate before gear retraction giving redundancy.
“Positive rate” (Altimeter increasing) for gear retraction is therefore the same for Take Off or a Go Around.

The IVSI, RA, Ground flight relay, Attitude and external visual indications are all useful for your situational awareness, however all have limitations.

7th Dec 2009, 13:10
Hi Kag,

I don't know what you operate, but most of my previous types have large doors which open to let the gear transit, then close around the extended gear. Hence 3 limiting speeds with the gear: 1) Extended, 2) Lowering, 3) Raising.

What's yours?
That one: The Boeing 737 Technical Site (http://www.b737.org.uk/landinggear.htm) (sroll down).

“Positive rate” (Altimeter increasing)
I agree with your post, just one thing (again) "positive rate" refers to the VSI, "positive climb" to the altimeter.
The VSI gives a rate (positive or not), the altimeter a climb or a descent.
I know this is a detail, please don' t be offended.

7th Dec 2009, 13:50
Hi Kag,

Sorry - I'd lost the initial thread of B737 - with contributions from B777, B747 etc. Thanks for the reminder that B737 doesn't have gear doors that close around the extended gear - I'd forgotten that.

8th Dec 2009, 20:47
If the houses, trees ,Moose are getting smaller, your going up, if the Moose is running like hell, houses ,trees getting bigger, your going down, works every time!

8th Dec 2009, 23:29
I am with a few of you here.....is this a serious question? Is this really worth the bandwidth?

9th Dec 2009, 05:24
This is an old conceptual problem which come from the begining of our careers.When you are at the flying school , since the GA airplanes have no RA , you are teached to check the V/S.Then you go to the medium jets and you continue using the V/S isntintively for all your life until the question arises.

In the medium jets , this is not a big deal since they are still short, but you can already note some erros ,despite V/S information is beeing provided by IRS.

When you go to the large jets, since the moment that you start rotating until the point you get your wheels flying take some time. It hapened to me srveral times , to hear from inexperienced pilots "posite climb" with the MLG still on the runway.

I take a look at the V/S , but the reference I really consider is RA.

7th Jan 2010, 16:56
two things which can help you determine +ve rate of climb...

1. listen to click noise of landing gear solenoid, which indicates that a/c has gone from ground mode to air mode.

2. movement of altimeter reading on the positive side.

3. IVSI a big NO.

hope it helps........

7th Jan 2010, 20:54
3. IVSI a big NO. If you had decided that IVSI +500 fpm would heed the call; is that still NO for IVSI or rather sensible use of the most precise instrument available?

All under the condition that you need/have to pronounce a "numeric" definiton of positive veritcal. As long as you are happy with the "gut feelin'" description all is well even with Mk1 eyeball/ears. Some actually need to standardize beyond such definiton.

FD (the un-real)

8th Jan 2010, 05:07
am adding another aspect apart from takeoff sit. what is considered as positive climb during upset recoveries / stall rec for getting gear up ?

A Comfy Chair
8th Jan 2010, 07:55
Eagle737 - I think you answered your own question.

"Retract the landing gear after a positive rate of climb is indicated on the altimeter."

That means the altimeter.

If Boeing had wanted you to measure positive rate of climb on another instrument, they would have stipulated that - or omitted the altimeter from the instruction.

Verifying it off all the other instruments is a good idea... but I can't help wonder why so many have a problem with just calling it off the altimeter as stipulated.

8th Jan 2010, 08:39
Why over-complicate things?

...only true words in this thread so far:zzz:

8th Jan 2010, 11:10
Hello! A-320 a/c. In my company SOP the positive rate of climb is when radio alt, vertical rate and pressure alt are going up.
Let's imagine a litle bit. You've just airbone so the first signe of the positive rate that you can see is radio alt changes (one second of time). Second, the most obvious, sign is VSI changes (another second). Third, the pressure alt changes, it is one more second. Next we confirm:"posituve climb" and PF order:"Gear up". Then PNF moves the gear leather up.
Totally we have ay least 5 seconds from lifting up to the begining of gear up preses. With the average speed is equal to ~500 f/m we will be at 41' above ground. so you don't need to worry about to early gear retraction.

Con respecto!

8th Jan 2010, 12:21
Isn't this alot of text for something I thik most of us do instinctively?

Youv'e gone through Vr and the nose is pointing skyward, the hairdryers are still operating and the seat of your pants and your eyes are saying you are climbing so you back it up with the relevant instrumentation your SOP's have indicated and call 'positive rate'