HI,

Just a quick question regarding the use of pressure error correction for adjusting the DA on an ILS.
In Bob's book on page 5.60 (July '11 edition) it suggests that for the Beechcraft Duches chart shown, at 75kt IAS you would need to add 2 feet to the DA. I would have thought it to be the other way around based on the notation on the chart suggesting you add 2 feet to the indicated altitude - ie if your indicated altitude is say 248 ft and your DA was 250 ft, you would add 2 feet to get your corrected altitude of 250 ft, or take 2ft off the DA to make it correspond with the indicated altitude.

I hope this makes sense, and I would appreciate it if someone could check my logic.

Cheers
David

David

The interpretation used by the IFR pilots I have spoken to is as follows.

PEC is Pressure Error Correction. So the value obtained from the chart is the correction, not the error. Therefore, if the chart says the correction is +2, it is telling you what to do to correct for the error i.e. add 2.

Now I must admit I have never applied PEC 'in anger', but most pilots seem to go along with that interpretation. It could be that I have it wrong myself, I'd be interested in any other opinions. In any case, I'm sure you wont be asked to actually apply PEC in the exam, the question will usually state that you have chosen not to apply PEC. It's adding the 50ft that the examiner is interested in. Wouldn't you agree that adding [or subtracting] 2 feet is a bit fanciful anyway. One tenth of one division on the altimeter scale - "Tell 'im 'es dreamin'!!"

Thanks for the post.

Bob

Thanks Bob for your reply.

I'm sorry if this is too pedantic to worry about, but in preparing for such an exam, you never know quite how pedantic your examiner will be.

I understand that it is a correction which needs to be added, but the chart provided suggests it needs to be added to the altimeter reading to correct it, not added to the DA which would have the opposite effect.

I agree the magnitude of the adjustment in this example is not operationally significant, I guess I was trying to preempt the potential pedantic exam question. It is encouraging that this is likely to be beyond the scope of a reasonable question.

Regards
David

OK. You are correct. I should have said in the text to add it to the altimeter not to the DA. I will change the wording in the next print of the book, Thanks for your feed-back. It is much appreciated.

Thanks again for your help Bob.

Regards
David.