I still feel bad about this, but one time I taxied a Boeing 747-400 for takeoff at the Victorville Airport (former George AFB, California) and was halted behind a Cessna 150 on the taxiway ahead of me. Victorville had no control tower (that is, it was “uncontrolled”) and the Cessna was not listening to the non-obligatory CTAF radio frequency. (CTAF stands for “Common Traffic Advisory Frequency,” a radio channel we often listen to so we can exchange information which improves safety.)

So we were trapped while the student pilot and instructor did their little airplane run up (engine checks) and completed their checklist and pre-departure brief. We couldn’t take off until they moved, either to clear a path for us or because they made their takeoff. So we were stuck, idling and sucking down a couple hundred gallons of jet fuel and looking at the scenery.

But it was 10am on a beautiful day! We had plenty of gas and were flying an empty airplane to Ft. Bliss/El Paso, Texas. We were happy and (the company’s fuel being burned their problem, not really mine) feeling wonderful.

The first officer, Larry Buckler, was a former 747-400 Captain himself and recently returned line pilot from having spent years as an instructor. He reminded me that some of the early -400s had a “Ground Crew Call” button on the overhead panel, and that pressing it sounded a loud horn mounted on the nose gear strut. In other words, in our jet we could “honk our horn” like a city bus!

A note about the Cessna 150: all that I have flown have a rear view mirror on the dash, much like a car. Crazy. Used like a car, you couldn’t see anything of value behind you but used by a flight instructor, I could adjust it so that I could see my student’s face — useful to determine your student’s stress/distress level in training. Still, most pilots habitually adjusted this mirror to look backwards.

I suppose that if the Cessna pilot looked in his rear view mirror, all he could see was a massive nose wheel strut (which weighed more than his entire airplane) and a big, sun blocking shadow.

I also recall getting a little closer than we should, maybe 50′ back.

We honked our horn. Just as a joke. We thought it was pretty funny. I’d watched a 727 Captain do the same decades before when I was a 727 flight engineer, and we all laughed back then.

The Cessna must have heard our horn because he suddenly powered up and shot ahead into a turn-out to make room for us to pass. To “get out of our way.”

Neither Larry nor I laughed in our big, elevated cockpit. We both realized it had been a stupid, inconsiderate thing to do to a new pilot, “beeping our horn” and surprising him that way. (Years before, both Larry and I had been student pilots. We had been instructors, even mentors. We felt an obligation to encourage new guys and especially in safe practices.)

To that guy from back in 2007, if you’re reading this: sorry about that. I apologize. We should have stayed behind you for as long as you needed to get safe, to be safe, before you committed to takeoff. Hurrying and risking death in a Cessna leaves you just as dead as screwing up in any other airplane. And by beeping the horn we inflicted upon your lesson a messed up adrenaline-based distraction, and that was our trespass.

So yes, some big jets have a “Ground Call” alert, which works like a car’s horn. Use it wisely, not like I did.

In some aircraft yes we have horns. It is most of the times used by us (pilots) to get the attention of the ground engineer. It mostly works two ways. In Airbus aircraft, the engineer can buzz the cockpit using the controls on the aircraft ground control panel and if he has his headset connected, he can establish communications with the cockpit.

The horn control switch on A320 is marked as ‘MECH’ which stands for mechanic.

The horn also have two other important functions (Airbus aircraft). One is that it will automatically beep, if the aircraft is shut down with at least one ADIRU (Air data inertial reference unit) turned on. The ADIRU is the primary navigation computer of the aircraft and there are three of them with each one directly connected to the aircraft batteries (HOT BUS) for safety reasons.

So, there is a chance that someone might leave the rotary knob of one of them in turned on position when they leave the aircraft thinking the aircraft is fully shut down. In this case, to make those near the aircraft aware, the horn will beep. If an ADIRU is left on, it will drain the batteries.

The next way by which the horn makes itself useful is by warning of an APU (Auxiliary power unit) fire. There are situations, where engineers work on the aircraft with the APU running but without any personnel in the cockpit. Here, if the APU were to catch on fire, the horn will come on, to grab the attention of those around the aircraft.

In the perfect world, the APU should automatically shut down and the extinguishers discharge. If it does not work, the engineers can force shut it down using the ground panel or by using the APU fire push buttons in the cockpit.