Setting heading indicator in climb?

[EightsOnPylons]

Hello,

I was just wanting an opinion regarding aligning the heading indicator with the magnetic compass during climb. In Europe I was taught to NEVER set it during climb, but here in the US I have been taught to do it.

As long as the aircraft is in a climb and not in an accelerated climb all the forces are acting equal upon the aircraft, and therefore the HI can be set? That is my opinion, please comment.

[Johnny 7]

I teach to align the DG/MC in level, unaccelerated flight only. The errors associated with the MC in a climb/descent due to tilting of the bowl & the relative accuracy of the DG during the same phase of flight should deem it unneccessary to realign providing you have compared RWY HDG, MC, & DG on the runway prior to takeoff roll & regularly during level flight.

I teach in the U.S & Europe.

[fireflybob]

It's a long time since I have thought about this one but I believe that the deviation of the compass is affected by pitch attitude - don't ask me why!

Perhaps best to ask the question on Tech Log - I am sure there is some boffin out there who knows the answer.

[Splat]

But is there not an argument that in the climb one should be concentrating more on engine instruments, airspeed, not busting alt, look out etc etc et. I realise a lot of these are also required straight and level, but in a lot of cases the workload is less, specialy for a student.

Splat

[ATPMBA]

From the FAA Instrument Flying Handbook, AC61-27C, page 50.

“Another common error results from failure to maintain straight-and-level flight while reading the magnetic compass for the heading to set in the directional gyro. Errors in the magnetic compass induced by attitude changes are thus duplicated in the heading indicator.”


I’m surprised a CFI told you differently as this is basic stuff that your need to know before going on cross-country flights. You should contact him/her and let them know in a nice way the correct way, before a student of him/her gets into trouble.

['I' in the sky]

I also remember at the beginning of my training being told that the compass is only accurate in "straight and level, unaccelerated flight".

Subsequent training for both CAA and FAA Cpls, IRs and Instructor ratings has then specified both turning errors and acceleration/deceleration errors associated with the compass but never an error caused solely by pitch, unless there is an associated acceleration or deceleration.

From a practical point of view it should not be necessary to align the Heading Indicator during the climb if you planned things properly prior to that, however I do not of a reason why for example if you are on partial panel in a straight constant speed climb that you should not be able to rely on the magnetic compass to confirm your heading.

I will ask ground school and see how many different answers I can get.

Okay first answer already.

No errors in a straight unaccelerated climb related to tilting of the bowl.

However due to the change in relative position of other components of the aircraft and engine in the climb attitude relative to the compass, and therefore changes in the three components of the magnetic fields which cause deviation there could be an overall change in compass deviation.

[Northern Highflyer]

Eights

I am assuming you are talking GA flying here ?

If so then the climb phase will only take a few minutes. If you have set your heading before the climb, in straight and level flight there should be no need to realign until the climb is complete. I would concentrate more on check turns to make sure my climb was clear of other a/c rather than the HI at this stage.

[fireflybob]

Apart from the technical aspect of deviation in the climb attitude, I quite agree with emphasis airmanship during the climb - "weaving" to clear blind spot under the nose etc.

What peeves me though are the guys who diligently synchronise the DI with the compass in the pre take off checks only to reset the DI to the runway heading after they have lined up for take off!!

[paulo]

Mr bob, there is some logic to this...

...compasses can be horribly wrong. Unless some joker has repainted the numbers, the runway is usually right.

This might sound a bit theoretical, but in the type I fly, the compass is ******ed if, for example, you have pitot heat on.

Of course you shouldn't have it on when setting DI on initial checks, but who knows. I never realised this 'throw' until the CFI mentioned it to me one day. 20 degrees 'ping!' on pushing that switch.

['I' in the sky]

Paulo,
When the guy first paints 21 on a runway the actual runway QDM can be anywhere between 206 and 214 degrees. After several years of annual change of magnetic variation the runway QDM could be well outside these limits.

I think what Bob is referring to is that scenario where somone lines up on Rwy 21, sees the Heading Indicator on 202 degrees and realigns it to 210 degrees. The compass meanwhile is also on 202 degrees.

Now where's the logic ?

[mad_jock]

I thought compasses were swung with the electrics associated with the cruise turned on?

Ie pitot heat on, radios on, etc

I was always taught to leave it alone until stable in the cruise

MJ

[Borat The Great]

The compass is swung with electrics on

The DI gyro is aligned with the North and South indications, it also has a certain ammount of freedom in that plane(whether its pitch on a north/south heading, roll on east/west or either one on any other heading. Gyro wont be affected by normal climb/descent attitudes, It has an Erection mechanism.

Compass errors (apart from liquid swirl) are a result of dip(Z) so in a climb/descent the needle may be more/less dipped (until it reaches the stops)

Unless I have misuderstood something, provided we are not turning or accelerating, or in a vertical climb/descent when the compas is no longer swinging freely, we can expect a sensible compass indication.