15
$\begingroup$

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?

$\endgroup$
  • 3
    $\begingroup$ 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 Jun 20 '17 at 15:09
  • 4
    $\begingroup$ 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 Jun 20 '17 at 15:13
  • $\begingroup$ Welcome to aviation.SE! $\endgroup$ – Pondlife Jun 20 '17 at 15:39
22
$\begingroup$

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.

| improve this answer | |
$\endgroup$
  • 1
    $\begingroup$ I agree, I've never selected anything but both in a c172, or had anyone say you should do otherwise. $\endgroup$ – GdD Jun 20 '17 at 15:14
  • 2
    $\begingroup$ 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. $\endgroup$ – 757toga Jun 20 '17 at 15:21
  • 2
    $\begingroup$ 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 Jun 20 '17 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 Jun 20 '17 at 20:44
  • 2
    $\begingroup$ 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. $\endgroup$ – 757toga Jun 21 '17 at 0:36
4
$\begingroup$

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.

| improve this answer | |
$\endgroup$
  • $\begingroup$ 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 Jun 22 '17 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 Jun 22 '17 at 16:38
  • $\begingroup$ @Gerry That is true, because the later models do have an electric fuel pump $\endgroup$ – J Walters Jun 22 '17 at 16:43
-1
$\begingroup$

Before landing, you should inspect the fuel qty indicators for and imbalance. If one exists, select the fuller tank, if none exists , select BOTH. You will want to minimize the weight imbalance between the tanks and have the engine help address this by burning off fuel from the fuller tank. You should also monitor your fuel levels in flight and make aproroate rank switches as needed th keep the fuel levels more or less even if an imbalance comes about with the valve on BOTH.

| improve this answer | |
$\endgroup$
  • 2
    $\begingroup$ The action you recommend here could lead to a violation of aircraft operating requirements since most C172 models are required to be operated with the tank selector on "BOTH" for takeoff and landing. $\endgroup$ – J Walters Jun 22 '17 at 19:18
  • $\begingroup$ And ignoring or not attempting to correct a weight imbalance would do worse, particularly in slow flight. $\endgroup$ – Carlo Felicione Jun 22 '17 at 21:41
  • $\begingroup$ The fuel quantity sensors are not accurate except on empty. Moreover, a fuel imbalance in a C172 is typically not a major concern. Selecting "BOTH" will typically help resolve the imbalance unless there is a tank leak or a major venting problem. $\endgroup$ – J Walters Jun 23 '17 at 4:18
  • 1
    $\begingroup$ No the gauges are only REQUIRED to be accurate when they indicate empty per regs; their indications may or may not reflect actual fuel levels. And no, selecting both will not resolve a fuel imbalance if for whatever reason the engine feeds more heavily from one tank. $\endgroup$ – Carlo Felicione Jun 23 '17 at 13:05
  • 1
    $\begingroup$ There are three primary reasons for an actual fuel imbalance when operating on "BOTH": A leak, venting problem, or sustained uncoordinated flight. The later actual imbalance will not be accurately measured by the C172 float sensors, and selecting the tank indicated to be most full will typically exacerbate the imbalance. $\endgroup$ – J Walters Jun 23 '17 at 18:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.