B737-200 go-around EPRs
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Joined: Aug 2008
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From: Europe
B737-200 go-around EPRs
I am currently preparing for the FAA ATP knowledge exam, and there is a question about the Boeing 737 for which I cannot find a satisfactory answer in the preparation books and Websites. So I thought that some of you may have some indications for me.
The question is about the B737 EPRs. I guess this is the old 737 as I believe that the new ones (with CFM engines) use N1, not EPR for engine power setting.
The FAA question gives some conditions (OAT, pressure altitude, air conditioning and anti-ice on or off) and a B737 table giving go-around EPR as a function of temperature and go-around EPR as a function of pressure altitude (every 1000 ft). The question is about calculating the go-around EPR.
The principle is quite simple, you calculate the temperature-limited EPR and the pressure-limited EPR and the result is the lower of both.
My problem is with the pressure-limited EPR. Let's imagine the question is about a go-around at 500 ft pressure altitude. From the table, you have the value at 1000 ft (2.04) and the value at sea level (1.98), so if you interpolate, the value at 500 ft should be 2.01. There the problem begins, because some books tell you to interpolate, but some others tell you that interpolating is wrong and that the value at sea level should be applied all the way to 1000 ft, as suggested by the arrow on the lower part of the graph. I am a little bit skeptical about the last explanation, first because I cannot see why you would set 1.98 EPR at 990 ft and jump to 2.04 EPR at 1010 ft, second because for the only EPR aircraft I've flown (the Dassault Falcon 20 with GE CF700 engines) we used to interpolate EPRs (actually they were already provided every 1000 ft, but the result is the same). So I would tend to believe that interpolating the table's values is the right way to compute the go-around EPR, but if I could have confirmation (or not), I would feel much more comfortable for the test!
Many thanks for your help.
The question is about the B737 EPRs. I guess this is the old 737 as I believe that the new ones (with CFM engines) use N1, not EPR for engine power setting.
The FAA question gives some conditions (OAT, pressure altitude, air conditioning and anti-ice on or off) and a B737 table giving go-around EPR as a function of temperature and go-around EPR as a function of pressure altitude (every 1000 ft). The question is about calculating the go-around EPR.
The principle is quite simple, you calculate the temperature-limited EPR and the pressure-limited EPR and the result is the lower of both.
My problem is with the pressure-limited EPR. Let's imagine the question is about a go-around at 500 ft pressure altitude. From the table, you have the value at 1000 ft (2.04) and the value at sea level (1.98), so if you interpolate, the value at 500 ft should be 2.01. There the problem begins, because some books tell you to interpolate, but some others tell you that interpolating is wrong and that the value at sea level should be applied all the way to 1000 ft, as suggested by the arrow on the lower part of the graph. I am a little bit skeptical about the last explanation, first because I cannot see why you would set 1.98 EPR at 990 ft and jump to 2.04 EPR at 1010 ft, second because for the only EPR aircraft I've flown (the Dassault Falcon 20 with GE CF700 engines) we used to interpolate EPRs (actually they were already provided every 1000 ft, but the result is the same). So I would tend to believe that interpolating the table's values is the right way to compute the go-around EPR, but if I could have confirmation (or not), I would feel much more comfortable for the test!
Many thanks for your help.
