Flying to Hawaii in a Cessna 172: A Complete Guide

An enthusiast with a small airplane is like a kid with a Lego block: it isn’t long before they’re asking themselves, “Where else can this thing go?”

A fellow aviator and I were chatting a while ago, and ended up discussing a juicy question: can a Cessna 172 fly to Hawaii from the continental United States?

A regular Cessna 172’s range of 734 miles is inadequate to fly to Hawaii’s closest airport, 2,297 miles from the mainland US. With extra fuel to extend range, 172s can fly to Hawaii from the mainland; such flights have been done, but require special planning, preparation and equipment.

If you’re wondering how you might fly a small, single-engined piston aircraft across the considerable expanse of Pacific ocean that lies between the US West Coast and Hawaii, without ending up in the drink… Well, wonder no more, because this post will explain exactly what such a journey would entail.

What Are the Requirements to Fly a Small Plane From the Mainland USA to Hawaii?

First things first: let’s define exactly where in the mainland USA we are going to take off from, where in Hawaii we intend to land, and which small plane we’re going to use to do it.

We’re discussing how to pull this off in a Cessna 172, but there are many 172 variants. For the purpose of this post, let’s use a 172S, the model currently in production.

Let’s also assume that we’ll be taking off at Little River Airport (KLLR) in California, because it’s the closest one to our destination that has refueling facilities, as well as a nice, 5,249-foot-long runway.

Our destination is Hilo International Airport (PHTO) in Hawaii, again, because it’s the closest. Flying direct from Little River to Hilo, gives us a flight distance of 2,297 miles (3,697 km).

With these assumptions in place, let’s answer the first big question:

How Much Fuel Would a Cessna 172 Need to Fly to Hawaii from California?

At the 172’s most fuel-efficient engine setting, it can cruise at an airspeed of 98 knots (112 mph / 181 kph). Assuming (for now) that the flight encounters no headwinds, tailwinds, or crosswinds that slow it down or speed it up, the ground speed remains the same at 112 mph.

Dividing the flight distance of 2,297 miles between Little River and Hilo airport by the 172’s cruise speed of 112 miles per hour, gives a flight time of 20.5 hours. For convenience, let’s round this up to 21 hours.

At its most fuel-efficient setting, the Cessna 172 consumes 6.9 gallons (26.1 liters) of fuel per hour. Given that there’s no place to land and refuel between Little River and Hilo, making this 21-hour flight would require the 172 to carry about 145 gallons (549 liters) of fuel on board, at the very least.

In fact, this flight would need much more than 145 gallons of fuel, because in reality:

1. it is guaranteed to encounter winds that affect its ground speed;
2. depending on the flight rules, the flight may not have direct routing, thereby increasing the distance and the fuel required;
3. the fuel consumption during the climb to the cruise altitude of 12,000 feet is much higher than 6.9 gallons per hour, and,
4. for both legal and safety reasons, it is necessary to carry more than the fuel required to reach the destination.

So, how much extra fuel will we need in addition to the 145 gallons? Let’s look at the legal requirements first.

As specified in part 91 of the Federal Aviation Regulations (FARs), the minimum fuel that an airplane must carry depends on whether it flies under visual flight rules (VFR) or Instrument Flight Rules (IFR). These rules govern the weather and visibility criteria under which a plane is allowed to fly, and they also have implications on the extent of assistance that air traffic control (ATC) will normally provide.

For a flight going so far over the ocean, it is much safer to fly under IFR, where the flight’s progress is monitored more closely by ATC. It’s never advisable to venture out over the ocean without ATC knowing where we’re going and when we’re supposed to reach our destination. (Any pilot attempting this flight must have an instrument rating, and also better have had special training on overwater procedures.)

Under IFR, an airplane must takeoff with enough fuel to fly to the destination, plus enough to fly to the alternate airport (just in case something goes wrong at the primary airport, like another aircraft stuck on the runway, for example), plus enough to keep flying for an additional 45 minutes at cruising speed.

The nearest alternate airport to Hilo is Waimea-Kohala Airport (PHMU), 45 miles (73 km) to the north west. Including the extra 45 minutes of holding fuel, this comes out to 10 gallons of extra fuel, putting our total at 155 gallons (587 liters) to fulfill IFR fuel planning requirements.

However, when attempting a 21-hour flight over the ocean with no place to land in between, we don’t want to fly with only the bare minimum safety margins, just to satisfy some rule in a book. The thinner our buffers for safety, the more likely it is that even a minor glitch — like a cylinder head temperature that starts running slightly too hot about two-thirds of the way into the flight — escalates into a serious emergency.

With greater safety margins, such an event would not be more than a slight inconvenience. If the aircraft can possibly carry it, it’s prudent to plan for at least 10% extra fuel over the minimum volume required to be legally compliant.

Therefore, in this case, the total fuel required for a Cessna 172 to safely fly from Little River to Hilo International Airport, is 170.35 gallons (645 liters).

This brings us to our first major challenge: in normal configuration, the maximum fuel capacity of a Cessna 172S is 53 usable gallons.

In other words, to fly from the continental US to Hawaii, a regular Cessna 172S needs more than 3.5 times as much fuel as its normal fuel capacity allows.

Luckily, this is still possible by installing special “ferry tanks”, although these will require the front seat and passenger seats to be removed to accommodate the extra weight. 170 gallons of avgas 100LL fuel weighs about 1019 lb (462 kg). This modification needs to be done professionally, and the aircraft must obtain a supplemental type certificate and be physically weighed, to ensure that the new configuration is within the safe envelope of the weight and balance limits.

With fuel sorted, let’s address the next challenges ahead...

Weather

The months between May and November are generally considered hurricane season in this part of the Pacific, so planning this flight well outside that window is prudent. Even so, this region can have unexpected storms and clouds throughout the year. In addition to extensive planning beforehand, staying abreast of weather changes with updates via radio is highly desirable (see “Communications” below).

Winds of about 15 mph (24 kph) at the cruise altitude of 12,000 feet are common, but they are often north-easterly or easterly, which works well as a tailwind that increases the ground speed of this flight.

Communications

Cessna 172s are normally equipped with VHF radios, whose range is restricted, more or less, to line-of-sight. Flying at 12,000 feet gives a VHF radio range of just about 135 miles, which is clearly insufficient on this flight. It’s therefore essential to equip the aircraft with primary and backup HF radios, which have a range of up to 2,000 miles.

It’s also a good idea to keep a backup headset — if your primary headset fails, it’s going to be difficult to endure the 85-decibel engine roar in the 172’s cabin for 20 hours.

Emergency Readiness

Nobody wants to end up in the water, but on the off chance that that does become necessary, it pays to be prepared. Being well-versed with the following tactics and equipment makes a huge difference, not just in the event of an emergency, but also to the peace of mind and confidence that comes with knowing you’re well-prepared:

• Ditching procedures
• Life jacket
• Inflatable life raft
• Survival suit
• First aid kit
• Flares and flashlights
• Handheld radio
• GPS
• Emergency Locator Transmitter
• Emergency Position Indicating Radio Beacon