Positive Rate

[tcasblue]

These quotes below(of which I have removed some info I felt to be non-pertinent were made on another thread.



Training for positive rate/climb identification is based on teaching pilots to recognise a positive V/S trend and increasing RA."

Two wrong statements in less than twenty words

Neither of these things are "positive rate". A V/S trend is a measure of vertical acceleration. It will happily read a positive vertical rate with both main gear planted on the runway with say, a gross error in take-off performance calculations or wind shear. RA is valueless for rate as the reading which the pilots see is a product of an algorithm of pitch attitude and gear tilt and is by no means a direct reading of actual height.

The ONLY measure for positive rate is a sustained and progressive increase in the altitude displayed on the altimeter.

Should you doubt any of this, consult any FCTM from a company called Boeing. They've been doing this stuff for quite some time.

Well said.

In addition to your reasoning, inertial vertical speed indicators will show a false positive rate of climb, on rotation.

Silver

Subsequently I found a note mine for a particular modern aircraft that says.....

VSI indication comes from the IRS, therefore when the nose is raised, there will be a positive climb indication even though the main gear is still on the runway.

So would most agree that the VSI is not a good instrument alone to use a determining a positive rate of climb for gear retraction after rotation and that the positive rate indication is initially due to the IRS moving upward.

[Intruder]

You NEVER rely on a single instrument! For the Positive rate" call, you use (as a minimum) VSI, altimeter, airspeed, pitch angle, and engine thrust, all AFTER the aural sounds of the relays clicking from the ground sensors.

[OK4Wire]

Nah, I just look out the front!

[Vessbot]

VSI indication comes from the IRS, therefore when the nose is raised, there will be a positive climb indication even though the main gear is still on the runway.


Wouldn't the old simple kind, be subject to the same pitfall since the static ports are in the nose area? I've never looked until after we're airborne, so I don't know but I think it stands to reason.

[Denti]

I often see an impatience by my colleague of the day about calling "positive climb". And i always wonder why. Normally all engines are working correctly, in which case there is absolutely no hurry to raise the gear at the first twitch of the VSI. And even with the often trained V1 cut it is better to assure that you are in a stable climb before raising the gear as it could be an even worse day if you do it on the first twitch and then some flying inaccuracy leads to a ground contact.

I was trained, quite long ago, to make sure by at least three independent sources that we are indeed positively climbing away from terra firma. Which seems to be a quite good idea in my mind.

[Goldenrivett]

"I often see an impatience by my colleague of the day about calling "positive climb"."

I wonder if those colleagues belong to this group? “Positive Climb”

[tcasblue]

Thanks,

Appreciate the replies. Hoping for a little more technical input about the IRS.

[Mad (Flt) Scientist]

The IRS position, relative to the nominal centre of gravity position, is known. The IRS can determine it's own movement, both in terms of translation and rotation. So it would be entirely possible to correct IRS data to any other position on the aircraft - and this is done in some experimental aircraft instrumentation setups. The error from having sensors very far offset from the centre of mass can matter. Though conversely, since the pilot is also not at the centre of mass, and it can be a pilot sensation you are interested in, sometimes you want the sensors offset.

So it is true that the raw IRS data is affected by the position in the aircraft, but that doesn't necessarily apply to any processed data.

@Vessbot - yes, the pitot/static system is going to be affected but the effect here is less that the static ports are moving relative to the ground and more that the aerodynamics around the nose is going to be changing as the aircraft rotates, and this effect is very much dependent on exactly where you are in the ground effect, and won't be exactly the same as the PEs you might see for similar angles of attack away from the ground. Obviously all depending on the specific design.

[B737900er]

The altimeter should be used to determine a positive climb as well as a IVSI. Look what happened with the EK crash a few years back. They had a positive climb initially then hit the deck a few seconds after when the gear was in transit. The altimeter would have moved only 50ft.

[vilas]

Airbus FCOM or FCTM do not give any guidance about where to check +ve climb.

[Denti]

Airbus FCOM or FCTM do not give any guidance about where to check +ve climb.

Yes, i was surprised when i discovered that. Of course, when reading this discussion i checked both the FCTM and the FCOM and found: nothing. Every little thing is defined, but not what positive climb exactly is.

And i just checked my old 737 FCOM (which is a pretty old version as i transitioned 6 years ago to the A320) and that is what it has to say:

"Do not retract the landing gear until a positive climb is indicated on the altimeter, preferably radio altimeter. Because of ground effect the altimeter may not show a positive climb until the airplane is 35 to 50 ft above the runway. Undue haste in retracting the gear is neither necessary nor desirable."

Especially the last sentence is in my view quite important. Otherwise, the result shown above might happen. Or a Dash-8 on its belly in SCN because the FO retracted the gear too early.

[Check Airman]

I flew with somebody a while back who obviously thought I waited too long to call “positive rate”. When he was PM, he’d make the call when we’d barley broken ground. Eventually, he’d start to call positive rate on his legs. It didn’t make me reach for the gear handle any sooner though. I never figured out what the hurry was.

[vilas]

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/2000x1058/img_20200624_141314_burst1_7aa04a67d64f284589be6b38d9a3956ff b824b05.jpg
The only guidance for +ve climb is this training DVD. It clearly says "When V/S positive and RA has increased". So not much theory in Airbus. In any case better be late than early.

[FlightDetent]

First large type, written in SOPs: Announce "postive xyz" after VSI indicates 500' fpm and RA is increasing. Smart people.

Simple and effective. Having read this and the previous thread, did not see any meaningful difference in other suggested techniques. Or any time on the line. Fits the Airbus snapshot too.

[Flutter speed]

Thanks,

Appreciate the replies. Hoping for a little more technical input about the IRS.

Little bit more info on the ADIRS that I can share.

The ADIRS calculates Inertial Vertical Speed and Baro Inertial Altitude. This Inertial Vertical Speed is what is shown on your PFD. It is not compensated for placement offsets wrt the C of G, a sudden rotation of the aircraft around the y axis (pitch up maneuver) will show as non zero V/S on the PFD.
The Baro Inertial Altitude is basically barometric altitude from the static ports augmented with the Inertial Vertical Speed. The latter is important since the V/S needs to be reflected on the Altitude Tape and vice versa. Also, integrating Inertial Vertical Speed to augment Barometric Altitude allows for a very quick and responsive altitude tape. Barometric sensors have considerable lag due to heavy filtering and their mechanics.

The filter loop is designed such that the altitude tape will always converge to the barometric altitude. Integration errors (due to accelerometer imperfections) will not result in a diverging altitude over long flight (obviously).

[Goldenrivett]

The Baro Inertial Altitude is basically barometric altitude from the static ports augmented with the Inertial Vertical Speed.

Always best to make sure the whole aircraft is positively climbing and not just the static ports.

[Uplinker]

Quite so.

It is really not very difficult to check that your IVSI is positive and your Altimeter and your Rad Alt are both increasing before calling "positive climb".

[Denti]

Quite so.

It is really not very difficult to check that your IVSI is positive and your Altimeter and your Rad Alt are both increasing before calling "positive climb".

Indeed. And there is absolutely no rush at all.

[hoss]

Keeping it simple and safe.

I know I use 3 things before opening my mouth to say positive rate and it all occurs in a couple of seconds.

SENSE: if I can hear T/O thrust and I can see the attitude passing through 12* I know that we are probably airborne.
and
INDICATION: check IVSI
and
CUE: my peripheral vision confirms for me the ground is getting further away.

”POSITIVE RATE”

[vilas]

SENSE: if I can hear T/O thrust and I can see the attitude passing through 12* I know that we are probably airborne. T/O thrust should have been not heard but seen and confirmed as N1 or EPR a long time ago. And it's not a matter of probability but a confirmation which comes from RA, normal altimeter and VS not from attitude.

[safetypee]

With the various views and procedures above, how, if at all, are they changed - applied in the event of an engine failure just after V1.

[deltahotel]

Can’t help thinking there’s some over complicating going on. Can’t answer for the Airbus, but Mr Boeing’s FCTM states ‘Retract the landing gear after a positive rate of climb is indicated on the altimeter.’ No more, no less.

Yes there are secondary and peripheral clues - the click of the lever lock, the houses getting smaller etc but Mr Boeing is the master of the art of keeping things simple.

safetypee - the wording in the FCTM is identical for the EFTO case.

rgds

[vilas]

With 50% loss of thrust the acceleration is less so rate of rotation needs to be slower and to a lesser attitude 12.5° in Air bus. Other than that everything else is same. RA and VS increasing raise the gear.

[Denti]

Just make sure it is not a momentary spike on the V/S, that could end very badly indeed... And yes, seen it enough in the SIM.

[hoss]

The EK777 crew may have seen a positive rate on their altimeters but did they ‘sense’ (sight, sound and touch) the G/A thrust coming on. Did it feel right.

Maybe I’m too over cautious with the positive rate call but I’m glad I take 1 second longer than the fastest pilot in my company.

[Uplinker]

The snag with the SOP of "positive RATE", is that the only cockpit instrument that gives a rate reading is the VSI/IVSI. Concentrating on the rate parameter might cause some pilots to only look at the rate indication, which might be false.

As the aircraft rotates, the static ports - usually situated around the front of the aircraft - will climb, even when the main gear is still on the runway, so this indication does not necessarily mean that the aircraft is climbing. Ditto the altimeter.

The Rad Alt aerials - on Airbus situated well behind the main gear - will inititally show a descent when the aircraft rotates.

Only when all three: VSI, Altimeter and Rad Alt are showing positive or increasing readings, can one be sure that the whole aircraft is climbing up above the runway. Take a moment to be sure all three indications are solid and not a momentary glitch, before calling positive CLIMB.

Another good reason for checking three instruments instead of one or two, is to check against a faulty instrument. All three should agree the aircraft is actually going up ! :ok:

[Vessbot]

The snag with the SOP of "positive RATE", is

...

Take a moment to be sure all three indications are solid and not a momentary glitch, before calling positive CLIMB.


Your valid point about overreliance on one instrument aside, you should use the callout verbiage that your SOP specifies.

[vilas]

Identifying +ve climb is not a big issue. The real problem is understanding priorities. Gear is not something that is to be got rid of as quickly as possible. I can't think of any incident where raising gear quickly or out of turn saved a disaster. It's other way round. In EK case if gear wasn't retracted aircraft wouldn't have been written off. On GA it's power, pitch, flaps then gear. On a low GA you hit TOGA, small change of pitch flap gear are left as they are till you are climbing away. No attempt is made to avoid ground contact because gear is the only part that can take impact load. Tail strike is more damaging.

[FlightDetent]

Only when all three: VSI, Altimeter and Rad Alt are showing positive or increasing readings, can one be sure that the whole aircraft is climbing up above the runway. That's pushing personal / company habits too far. Sinner like me can tell, as long as it is other people who are guilty and not yours truly. :)

And also factually incorrect.

[Pugilistic Animus]

It's a positive rate when the dog on the flightdeck starts trying to bite your hand
:}

[safetypee]

dh, #22, :ok:
Same procedure checks and calls, but with an engine failure and a performance limited departure, the timing of the checks and altitude of gear retraction need to change.

vilas, 'Gear is not something that is to be got rid of as quickly as possible'; so what triggers the change in thinking with engine failure, … the dog,

but PA's dog dies with engine failure; surprise of the event, forget, revert to everyday habit.

[transducer]

The Airbus FCTM>Procedures>Abnormal and Emergency Procedures>ENG>Engine Failure after V1, states the following under the "WHEN SAFELY AIRBORNE" heading:
With a positive rate of climb and when the radio height has increased, the PM will call "positive climb". This will suggest to the PF for landing gear retraction.

[RVF750]

There are VERY FEW things on the flightdeck where rushing helps at all. In sim sessions, it's always rushing that causes issues. Even the swing of the normal V1 cut isn't immediate in a hi-bypass jet. Just take it easy, check and double check and satisfy your inner SA all is as it should be, then act.

It's always worked for me.

[Mad (Flt) Scientist]

Just out of curiousity, has there ever been an incident (let alone accident) where a crew dawdling in raising the gear (but doing so eventually) has caused the problem? I can't offhand think of one.

The reality is that even single engine performance has margins built in, and considers a case usually much worse than the case of the day. I'd be really shocked if an extra, say, 5 seconds in initiating gear retraction in any remotely routine OEI condition represented a meaningful safety reduction.

[Check Airman]

Just out of curiousity, has there ever been an incident (let alone accident) where a crew dawdling in raising the gear (but doing so eventually) has caused the problem? I can't offhand think of one.

Define "eventually":E.

I can't find an actual report on this incident.

https://www.ajc.com/news/national/airliner-forced-land-after-pilots-accidentally-leave-landing-gear-down-for-entire-flight/YCu3nXWUl3367aYfQHffMJ/

[vilas]

​I can't find an actual report on this incident.​​​​​​ The link you posted is good enough. That's all happened. Fortunately while landing at the diversionary airport while putting the gear down they realized the gear was already down and left it down. Otherwise had they acted on it mechanically that just change the existing status then it would have been more interesting.

[Goldenrivett]

Fortunately while landing at the diversionary airport while putting the gear down they realized the gear was already down and left it down.

There is a recognised human error called "action slip". If you have ever tried to make a cup of tea by pouring the boiling water into the tea caddy rather than the tea pot or put your keys down in an unusual place so you can't locate them - then you have performed an action slip. If you haven't yet - then most probably you eventually will.

A more serious action slip is moving the flap lever instead of the gear lever. G-EZOZ (https://assets.publishing.service.gov.uk/media/5c111535e5274a0bc44dcd5a/Airbus_A320-214_G-EZOZ_01-19.pdf)

Usually an alert crew will recognise the error and fix the problem. Sometimes if overwhelmed by other distractions e.g. overspeed warnings, "terrain ahead pull up" etc. then the action slip of moving the gear lever in the wrong direction may (did) go unnoticed. But WTF did the crew of PIA 8303 not GA at 500 feet?

[Check Airman]

There is a recognised human error called "action slip". If you have ever tried to make a cup of tea by pouring the boiling water into the tea caddy rather than the tea pot or put your keys down in an unusual place so you can't locate them - then you have performed an action slip. If you haven't yet - then most probably you eventually will.


Ah. So that’s what that’s called. I always thought it was called “getting older”. Really can’t relate to the tea example though. I’m not sufficiently British ;)

[hans brinker]

Define "eventually":E.

I can't find an actual report on this incident.

https://www.ajc.com/news/national/airliner-forced-land-after-pilots-accidentally-leave-landing-gear-down-for-entire-flight/YCu3nXWUl3367aYfQHffMJ/


The link you posted is good enough. That's all happened. Fortunately while landing at the diversionary airport while putting the gear down they realized the gear was already down and left it down. Otherwise had they acted on it mechanically that just change the existing status then it would have been more interesting.

Well, in their "defense", they had two working engines....
Also for what happens with just "changing the existing status", see the Karachi thread (IMHO).

[vilas]

Goldenrivette
I would consider it as a Pavlovian conditioned reflex. In 70s there was an incident of Russian fighter jets landing gear up. The aircraft came in for landing the gear was seen to be down but had to go round. In second approach landed wheels up. In inquiry pilot was sure he had lowered the gear in downwind. Actually he had forgotten to raise the gear after missed approach and in downwind he thought he is putting it down but in reality he had raised it. PK8303 actually confirmed a lot of human factors.

[vilas]

Well, in their "defense", they had two working engines....
Also for what happens with just "changing the existing status", see the Karachi thread (IMHO).
Since they had Engines and they were not in panic possibly they would have noticed too low gear and gone around.

[Uplinker]

Keeping it simple and safe.

I know I use 3 things before opening my mouth to say positive rate and it all occurs in a couple of seconds.

SENSE: if I can hear T/O thrust and I can see the attitude passing through 12* I know that we are probably airborne.
and
INDICATION: check IVSI
and
CUE: my peripheral vision confirms for me the ground is getting further away.

”POSITIVE RATE”

My guess is that you are joking, but as pilots, we need to measure positive climb, not merely think it seems to happening.

Hearing the engines are at T/O thrust ???? Probably airborne ????

+12° pitch might not get you off the ground if you forgot the flaps, or your engines are not at T/O thrust, or your speed is too low.

Peripheral vision is not reliable at night, or in low vis, or at airports such as Luton, Leeds or Jersey and others which have steep drop-offs after the runway, so the ground will fall away but that does not mean you are climbing.

The whole point of the positive climb call is that it confirms, by measurement, not by assumption - that the aircraft is climbing.

IVSI indicating positive rate + RA increasing + Altimeter increasing = Aircraft is climbing :ok:

[ScepticalOptomist]

IVSI indicating positive rate + RA increasing + Altimeter increasing = Aircraft is climbing :ok:

This! Anyone who flies an airliner that does it differently should change career.

Everything else is a cue, the above quote is the confirmation.

[nervous_novice]

This! Anyone who flies an airliner that does it differently should change career.

Everything else is a cue, the above quote is the confirmation.

lols, yeah exactly!!