The amount, types, duration, and severity of pilot stressors vary widely. The individual airline, union involvement, scheduled versus non-scheduled, international or domestic, type of equipment, freight or passengers, everything has an effect. I look at pilot stress within the context of what I was doing the last 10 years of flying 747s on international routes for two carriers. For me, the stressors usually (but certainly not always) were of three types: physical abuse of the body, decision making in the face of incomplete information, and frustration over things I had little or no control of. The examples below are from the 1990s, but I'm reasonably certain like things and conditions still occur. There are still 747-200s flying, not many, but two of them are SAM 28000 and SAM 29000, the President's two 747s (heavily modified of course).
Physical Abuse of the Body
For me the biggest stressor was the massive time zone changes. The last five years I was based out of JFK, but I lived in Oregon. After I collected a little seniority, I typically had 12 days off in a row each month, but a day of that on each end was given over to commuting.
Thus a work period began with the hassle and uncertainty of jumpseating for a multiple leg, minimum 2500 mile journey and a 3-hour time zone change to JFK. The most typical next day was JFK to Tel Aviv, a 12 hour flight and another 7-hour time zone change. We left JFK in late evening, arrived at the hotel in Tel Aviv in early evening of the next day. I would wake up in Tel Aviv around 0200 local, and from that point on through the rest of the work period, my circadian rhythm was totally screwed up.
We did a lot of charters, and that introduced a great deal of irregularity into our schedules. It was not uncommon to have a charter come up that would take us off the line that we bid for and was awarded, and from that point on we usually did not get back to the awarded line. Thus we often would not know what we would be doing after we completed the current flight until we got the call in the hotel after the flight.
If you operate often into third word countries, you may occasionally get sick. It happened to me twice in 10 years, once in Jakarta at the Hilton, and once in the Ramada just off the airport in Delhi. The Jakarta Hilton had a 24/7 clinic in the basement, primarily for their employees but available to their guests, so it was no big deal to have a doctor come up to my room in the middle of the night and give me a shot to control the vomitting and diarrhea and stop the dehydration. The Ramada was a much smaller hotel, so they had to call out a doctor from home, again in the middle of the night. We had no reserve captains in Delhi. I operated a Hajj flight the next day with a hand towel arranged as a diaper.
Decision Making in the Face of Incomplete Information
This happened all the time. It was part of the job, took many forms, and meeting the challenges was part of the fun, but it was stressful. For example, we picked up a planeload of U.S. Army troops at Stewart Air National Guard Base in New York to take to a recently constructed runway in the Balkans. We fuel-stopped in Paris because we had to have enough fuel to get out of where we were going. There was no fuel there. There turned out to be, in fact, nothing there but a very narrow, short (for a 747) runway surrounded by farmland, no buldings save for a couple of construction trailers. I wasn't given the information for the destination until just before departure in Paris. Enroute from Paris, looking at the approach plate and runway data, I saw two problems. The destination weather was forecast to be overcast, but with the ceiling high enough that we would be able to get in using the only approach aid available, an NDB. However, the airplane we had been dispatched with had an ADF that had only a pointer bug rather than a full needle. Our ops specs prohibited NDB approaches without a pointer needle with a tail. I ignored that problem. The second problem was that the taxi chart showed a runway too narrow to turn around on without getting a wing gear off the edge. There were no taxiways, no turnarounds, no ramps. This caused a series of contacts on HF via Stockholm Radio (no Satcom on this old airplane) between myself, dispatch, and our director of operations. The final call from the DO was to tell me he had talked to the military and that though the airport plate didn't show it, there was now a small ramp at each end of the runway. We landed, unloaded, and departed without incident.
Frustration Over Things I Couldn't Control
This category was large, most minor, some laughable even, some of more consequence, but all for me irritating. Things like being lied to by ground support people, crappy accommodations (I and a flight engineer got body lice from a stay at the Hotel Carrera in Santiago, Chile), having to pay bribes (especially in Indonesia and Egypt), having to sometimes wait hours for immigration clearance, often having to first say "salaam alaikum" on initial contact with Saudi Arabian controllers before they would answer , having to switch back and forth between saying Bombay or Mumbai during the name switch. Hindu nationalist controllers wouldn't answer unless you said Mumbai, others wouldn't answer unless you said Bombay.
The incident I most remember in this category is when I, a first officer, a flight engineer, and 14 flight attendants commercialled to Medina, Saudi Arabia to pick up a flight. After we got there, we were told the airplane was going to be at least 12 hours late. No problem, hotel time, as the rule was we were entitled to a room if there was to be more than a five hour delay. However, problem, there were no available accommodations in the airport area. There were rooms available in the city but, like Mecca, non-muslims cannot enter Medina. We sat for 14 hours in a terminal with pathetic air conditioning in the middle of summer before the airplane arrived.
One final small irritant. We kept having to give up our usual parking area at Tel Aviv to SAM 28000 and SAM 29000 during the latter months of Bill Clinton's time in office as he was making last ditch efforts to broker an Israeli-Palestinian peace.
So, stressful, definitely, but it was the highlight of my life, and I'm glad I did it all, including all that wasn't so great at the time.