how to determine "positive rate of climb "
 

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!

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.

GF

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?

or any Boeing expert can explain this?

Sorry, not a Boeing expert. Our book just says "positive rate of climb".

GF

From PanAmerican, long ago...

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


vsi/ivsi...No
Rad Alt.. No.

Pressure altimeter...Yes.

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.

Greetings
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:

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

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.

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".

Isn't a climb by very definition positive? A negative climb would be a descent would it not?:):)

Greetings, I think that the Altimeter alone is not enough, because maneuver induced error may still be hanging around :E

I look out the window.

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.

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.

For my info
 

Sorry to butt in but presumably there is an interlock to stop retraction if there is a load on the gear, ie oleo compression ?

There is, its called a squat switch. If its serviceable you have no worries but there have been many retractions on the ground.

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.

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!