During climb, what is rate of climb position?

[Sangman yoo]

Dear sir.

I know that during a/c climb, rate of climb indicator is climb position.
But my pilot said that about 4minute after take off indcated decent posion.
Why do this situation?
I think about that promblem is out flow valve failure and bleed pressure is low.
Have you ever generated this action?
if you understand this problem, please give me some advice.
I still stuff.
thank you for leading my message.

Have a nice day...

[BOAC]

OK - I'll try. Outflow valve shut or DPCS/CPS system failure. Nothing to do with bleed pressure.

How long was 'descent' showing? Changing altimeter setting can cause a momentary descent. What did the pilot do?

[Northbeach]

I know that during a/c climb, rate of climb indicator is climb position.
But my pilot said that about 4minute after take off indcated decent posion.
Why do this situation?

You did not mention what type of aircraft. I am going to assume it is a pressurized jet aircraft and that when you say "rate of climb indicator" you are talking about the cabin pressure rate of climb indicator and not the aircraft vertical speed indicator.

What was the altitude of the departure airport; was it a high altitude airport say like Mexico City > 7,000? What was the altitude of the landing altitude, was it much lower than the departure elevation? What was the cruise altitude set in the digital pressurization controllers flight altitude? Not having the pressurization panel set up correctly can lead to "different" readings.

If you take off from a relatively high altitude airport with the intention of landing at a much lower altitude airport it may be normal for the rate of climb to indicate a descent after takeoff as the cabin controller is pressurizing for the scheduled differential and the landing altitude. When we depart out of Mexico City for a sea level airport several hours later the cabin will initially indicate a descent during the climb out phase.

The flight did not take off unpressurized and then airborne the packs selected on was it? If you take off unpressurized, for performance reasons, then select the packs on you will get the descend indication while the jet is climbing. Under that condition it would be a normal indication.

It is possible that your outflow valve is sticking and not responding to the inputs from the pressure controller(s).

When I depart a sea level airport and climb to altitude passing through 10,000’ the cabin altitude is at approximately thefirst index mark off zero well below 1,000’, passing through FL180 the cabin differential is about 6 (If it were a clock it would “look” like 1:30 +/-). At FL350 the cabin should be around 7,000 +/-, there is a placard on the pressurization panel for reference. Did your jet pressurize on schedule?

[Sangman yoo]

Dear sir.
Thank for your return message.
I'm english composition very poor. but I'm pleased with understanded my opinion.
Our aircraft type is B737-800NG. pressurized aircraft and during take off, pressure system is auto mode.
pilot said that cabin altitude and differential pressure indicator is normal operation.
Out flow valve is normal operation. during flight have not a pain in the ear.
our country is about same sea level in depart and arrive.
I think that the cabin rate of climb indicator read that wrong.
I really concerned about this situation.
I'm a maint mech so i just thinking of this section.
I would like to ride to the simulator.
thank you for your help.
good luck.

[DongJoon Choi]

Cabin pressurization problems are caused by leakage, low bleed duct pressur, OFV and CPC, and defective bleed air system leads to the majority of the defects

If either engine duct pressure is very low during climb, rate of climb will
be much higher than normal and cabin altitude will increase rapidly. However, if both engine bleed pressures return to normal operations. CPC would modulate OFV to decrease cabin altitude, so rate of descent indication may be shown.

[Northbeach]

I'm English composition very poor

Your English is much better than my, or most of here on PPRuNE, command of the Korean language. I respect your effort in trying to get your question answered.

Are you sure your crew took off with the Packs in Auto and not off. This would be the case for a bleeds off takeoff, improved climb. Or perhaps they departed with the Packs off, forgot, made a mistake (it's been done more than once).