Alternate static source and compass q's

[Singlecoil]

Now...are you flying a C-172? Go to the Performance charts in Section 5 for Airspeed Calibration using the Alternate Static Source. In the FAA configuration, is the pressure higher or lower. Well the inside cabin pressure is higher because the airspeed corrections all move lower. We all know that the Airspeed is measuring the difference between RAM and static pressure - if the speed is "indicating" less then there must be less of a difference (i.e. the pressure is higher inside).

Huh? I don't have the chart in front of me, but if the corrections move lower, that is because the airspeed is erroneously indicating high. Pull the alternate static and you will notice airspeed higher than normal, altitude higher than normal, and VSI momentarily indicates a climb. All indicate lower than static pressure in the cabin. Read the airspeed indicator, apply the correction from the chart (to lower the figure you are seeing) and be on your merry way.

 

[supsup]

Compass Turns

Try this CEO. Take the obs or adf and put north on top. Now I use UNOS, Undershoot North Overshoot South. Only be concerned with what heading your turning to and from what direction. Back to the OBS, super impose 30 at North, 20 at 330, 10 at 300, 0 at 270. For example turning right to a heading of north you would roll out on a heading of 330 (Undershoot by 30 degrees). For south heading it works the same, 30 at 180, 20 at 150, 10 at 120 and 0 at 090. Turning right to a heading of 180 would require the mag compass to read 210 degrees.

supsup

 

[midlifeflyer]

It's kind of humorous to me, but the FAA, through the practical test standards (PTS), doesn't test us on what really happens with the magnetic compass--only timed turns.

I always wondered about that. I got my instrument rating about 10 years ago and my CFII taught me both methods. I always found compass turns easier and did them exclusively on my checkride with no problem.

The mnemonic I ended up using instead of the standard "South Leads, North Lags" is the same ANDS we use for acceleration compass errors, but in this case its,

Anticipate North, Delay South

 

[atldc9]

Believe it or not, I had to do compass turns on my last FAR 121 PIC checkride. The Boeing 717 has a standy instrument, called an ISIS, that provides attitude, altitude, and airspeed information in the event all other cockpit information is lost. It is a electronic presentation that is totally independent of all other cockpit systems. BUT, it does not provide heading information!!!! If ypu find yourself in a situation where you are down to the ISIS, which is very unlikely, like 10 to the 999th, you would be stuck doing compass turns. When flying one of the most advanced flight decks in the air today, the last thing you expect to do is compass turns. What was standard rate again?

 

[PennEagle]

Compass Turns

Well, here I am looking out the window at probably 2400RVR and VV001. So..... it's either go and do my taxes or wax lyrical on compass turns ......

I use "never see north" and "sail through south" when teaching compass turns. So, if bloggs is looking to turn from 360 to, say, 240, he's going to sail through 240 to a heading 245 (5 deg correction at my latitude) to settle out on the correct magnetic heading. Likewise, if (s)he wants to turn from 180 to, say, 060.... (s)he will never see 060 on the MC and should turn to a heading 080 (again, at my latitude).

Corrections are:

North ... ... ... Lat. + 7 deg (1/2 angle of bank)
330 or 030 ... 2/3 Lat. + 7 deg
300 or 060 ... 1/3 Lat. + 7 deg
270 or 090 ... Nil
240 or 120 ... 1/3 Lat. - 7 deg
210 or 150 ... 2/3 Lat. - 7 deg
South ... ... ... Lat. - 7 deg

An excellent exercise is to fly the plane yourself, and let the student really study how the MC behaves on a full standard rate turn. The MC can appear to be stationary for an awefully long time in certain heading/direction combinations, and at other times be doing Mach 2. Students who glance only briefly at it without understanding how it behaves can roll out early or late.

Finally, here's a fun question from my CFII oral before I go back to watching the snow ..... You are S&L heading 270 when you lose all your instruments in IMC, except the MC. The AP is on and you decide to climb at a constant IAS to known clear conditions. What does the MC read during the climb, a) West, b) South of West or c) North of West.