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On a recent checkout on a C172 I was told to select "fullest tank" as opposed to "both" that I have been doing for years. Given the aircraft is high wing (gravity feed) with no auxiliary fuel pump there should be no chance of sucking air.

Anyone know the correct selection?

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    $\begingroup$ What is the model and year? E.g. Cessna 172N 1977 has a special checklist and may be somewhat different than other models manufactured in different years. I would advise that you purchase a Pilots Operating Handbook for the relevant aircraft to find checklists/standard procedures. $\endgroup$
    – TayE
    Commented Jun 20, 2017 at 15:09
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    $\begingroup$ That was bad advice. The high-wing Cessna should ALWAYS be on BOTH for take-off and landing. It would be good for that CFI to be corrected. $\endgroup$
    – STWilson
    Commented Jun 20, 2017 at 15:13
  • $\begingroup$ Welcome to aviation.SE! $\endgroup$
    – Pondlife
    Commented Jun 20, 2017 at 15:39

2 Answers 2

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You should check your POH but it may just be that the instructor in question was recently flying a lot of Pipers and it was force of [bad] habit.

This POH for the 172S is in agreement with you.

BEFORE LANDING

....

  1. Fuel Selector Valve -- BOTH.

You should consult the checklist in the POH that is with the airplane in question to be sure.

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    $\begingroup$ I agree, I've never selected anything but both in a c172, or had anyone say you should do otherwise. $\endgroup$
    – GdD
    Commented Jun 20, 2017 at 15:14
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    $\begingroup$ C 172N checklist shows "Fuel Selector Valve - Both." There are some very important reasons why a high-wing, non-fuel pump, Cessna requires (for normal ops) to set the fuel selector valve to "both." Always check the POH. $\endgroup$
    – user22445
    Commented Jun 20, 2017 at 15:21
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    $\begingroup$ Appreciate that Dave, as it happens the operation have four Robin DR400's, two PA 28's and access to one C172. I will gently mention the "both" requirement next time I visit (as I'm reading the POH) $\endgroup$
    – 3GREENS
    Commented Jun 20, 2017 at 17:06
  • $\begingroup$ The only time I ever selected anything but "both" in a 172 is the one time I (foolishly) took off with a fuel imbalance. But even then, it would have equalized under "both". $\endgroup$
    – David Schwartz
    Commented Jun 20, 2017 at 20:44
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    $\begingroup$ Years ago I towed a banner for 3 hours over a football game banking left 90 percent of the time over the stadium in a C172. Got low on fuel on the right side then, after the job was up, I selected the left tank to balance the fuel on the way back to my home base (but, of course, selected "both" for landing. $\endgroup$
    – user22445
    Commented Jun 21, 2017 at 0:36
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Yes, the fuel selector typically must be selected to "Both" for takeoff and landing.

The Cessna 172 Type Certificate Data Sheet (TCDS) requires a placard for most early serial numbers (all models through S/N 17265684 except 17261445 and 17261578). This placard is to be located forward of the fuel selector valve and must state:

Both tanks on for takeoff and landing.

Note that this placard is required by certification for airworthiness, constitutes a limitation, and is to be followed by the pilot. See 14 CFR 91.9:

§91.9 Civil aircraft flight manual, marking, and placard requirements. (a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.

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  • $\begingroup$ The TCDS only covers C172 models through C172Q and the S/N statement identifies the placard as a requirement only for models through C172M. (The two S/N exceptions are C172N models.) The C172R and later are under a different TC. $\endgroup$
    – Gerry
    Commented Jun 22, 2017 at 16:27
  • $\begingroup$ Correction to my comment. The later models are under the same TCDS. It's just that you need to get TCDS 3A12 Rev 84 to see them. In any case, the placard requirement only applies through the M models. $\endgroup$
    – Gerry
    Commented Jun 22, 2017 at 16:38
  • $\begingroup$ @Gerry That is true, because the later models do have an electric fuel pump $\endgroup$
    – J W
    Commented Jun 22, 2017 at 16:43

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