Over the years I’ve heard of many musicians who are afraid of checking their instruments when flying. Musicians are afraid of rough treatment by airport baggage handlers, and rightly so. But many people also fear that the environmental conditions in the aircraft’s baggage compartment can damage their instruments. I asked some airline captains about the conditions inside aircraft that instruments with be subjected to. Their answers are very reassuring!

When travelling with instruments people worry about the effect of temperature in the aircraft baggage hold on their instruments. Outside air temperature at 35,000 ft may be -50 ºC/-60 ºF! Thankfully no part of the cabin or luggage hold of a modern aircraft ever gets close to freezing point. On modern passenger aircraft the entire aircraft interior is pressurised and the baggage hold is ventilated by the same air that the passenger cabin uses. Though the baggage hold (or a part of it) may not be directly heated, it is very well insulated against the outside temperature, and the warm cabin air prevents the overall temperature from dropping very far. On the smaller passenger jets, the hold may also be indirectly heated through the floor of the warm cabin above it. So the temperature in the baggage hold will never drop very low, usually not much cooler than about 8°C/46°F.

Have you ever picked up your luggage after a flight, and said “Oh my god, my bag is freezing cold!”? No. Ever opened your suitcase and found your shampoo frozen? No. Now you know why.

Even then remember that 8°C/46°F in the hold does not mean your instrument will reach that temperature. On short-haul flights of an hour or two, the temperature of your instrument may not drop much more than it does when you’re out about town. A well-packed and protected instrument is also well insulated and the temperature of the instrument will change slowly than its surroundings. That’s a good thing because the speed of the temperature change is much more important than the absolute temperature. Sudden, large changes in temperature can cause cracks in the finish as the varnish, paint, and woods all expand or contract at different rates. But slow temperature changes avoid those problems. Even on very long flights, if the instrument does get very cold, the change will be slow enough not cause us any problems. If after travel your instrument case is noticeably cold (or warm) to the touch, leave it for a few hours to come to room temperature before opening.

Also note that low temperatures are less problematic for instruments than high temperatures. When things get hot, such as leaving your instrument in a car for hours on a summer’s day, glue joints can soften to the point of failure under all that string tension. But that’s not an issue with cold. Your instrument is perfectly safe, provided you allow it to return to room temperature at a reasonable rate.

So, temperature on board an aircraft is not a problem. What about humidity?

Airliner cabins are dry places. At cruising altitudes of 35,000 ft there is virtually no water in the air outside the aircraft (planet Earth is very wet down low and very dry up high). Passenger airliners typically take 50% of the cabin air from that frigid, dry, outside atmosphere. This outside air is heated as it passes through the engines and air conditioners, and mixed with existing cabin air, which is recycled through hospital-quality air filtration systems (you are less likely to catch an airborne virus on an aircraft that in an office or cinema). The end result is cabin air that is very clean but also very dry, usually between 10% and 20% relative humidity. That low humidity can bother some passengers who will experience dehydration and chapped lips.

Excessively high or low humidity can of course also affect an instrument. In high humidity conditions, wood will absorb water from the air, causing it to swell slightly. In low humidity conditions, the opposite occurs: wood will give up some water to the air. Different woods will do this at different rates and each piece of wood will do it in different directions relative to the grain. As a result there can be changes to the neck relief, and to the shape of the top and back of hollow-body instruments. This can cause unwanted changes in string height, and neck and fingerboard woods may shrink slightly resulting in frets protruding from the side of the fingerboard (known as ‘fret sprout’).

Fortunately, these changes to the wood are reversible and easy to deal with. They are also slow to occur: in much of the continental US in mid-July, humidity may be 85% in the early morning and drop to 40% in the evening, yet we don’t have to adjust our guitars’ truss rods or humidify our instruments during the course of each day. A well packed and protected instrument will not only be less sensitive to surrounding temperature changes but humidity changes will present little if any problem. And if you are worried, there are numerous cheap instrument case humidifers on the market that can give you more piece of mind.

The last thing to mention is air pressure. When we talk about a aircraft being pressurised, we mean relative to the outside air at cruising altitude. But the pressure we experience inside an aircraft is less than what we experience on the ground. When cruising at an altitude of say, 35,000 ft, the pressure inside the aircraft is equivalent to an altitude of about 6,000 ft. That’s about 20% less than air pressure at sea level. Fortunately, instruments are not sensitive to changes in air pressure, only to the changes in temperature or humidity that go with it. And clearly, there a great many cities in the world at similar altitudes, or higher, and our instruments suffer no undue effects: Mexico City is at an altitude of over 7,200 ft, higher than most airline passengers ever experience.

I’d like to give you another perspective on this issue which you may not have thought about before: tens of thousands of people happily buy guitars and similar instruments online every week. Many of those instruments are shipped directly to the buyers’ homes, often large distances involving international travel. Have you ever wondered what environmental conditions those instruments are subjected to?

If we are shipping an instrument during the cold of a Northern hemisphere winter, instruments can be exposed to far greater extremes than flying on a passenger jet can do. Trust me, I’ve seen it! Your instrument may spend a significant amount of time in unheated warehouses, in the back of a unheated delivery trucks, or even on a shipping palette sitting outdoors in subzero temperatures (such as on the tarmac of a cargo terminal, waiting for loading), protected from the elements by only the thinnest of plastic sheets and a thin sheet of cardboard. Then it is abruptly moved into a heated handling area, or store, or your home. During the summer those shipping palettes may sit for many hours in heat and blazing sunshine before moving to cool air-conditioned space. None of this poses any great problem to these instruments. Adequate packing and protection is key.

Clearly, when the environmental conditions on passenger airliners are pretty benign for instruments, there is no reason to fear putting your instrument into the baggage hold of an aircraft provided you have it adequately packed and protected, particulary against the dangers of baggage handlers! I’ll deal with those issues and options for travelling in an upcoming blog post. Stay tuned!

With thanks to Captains Barry, Rick, Spike, and BUC for their valuable input!