Two fully qualified pilots in the front can work well together, or it can be worse than having a “back-seat driver” right next to you.
Commercial aviation almost universally relies on two-pilot operations for safety. These pilots are trained to work together well, to ritualistically cross-check each other, to share some of the workload.
In the recreational part of general aviation however, pilots are trained to work alone. For someone to earn an instrument rating on a complex aircraft, they must be capable of swallowing a firehose spew of work, including concurrent simulated emergencies and instrument approaches. To cope, people develop routines about what to do when, how. There is rarely excess intellect for improvising a workable routine during a flight examination.
But what to do then when, as luck should have it, two private pilots share a cockpit? Since pilots are social animals and love to show off their toys, it’s not uncommon to go fly together. I generally try to bring along another pilot for GXRP, as a favour of providing loggable twin-engined experience for them. But since neither of us is generally given any formal training for two-pilot routines, it can get clumsy.
For example, the pilot “not flying” (with free hands) may feel an urge to be helpful during a flight, doing work associated with checklists slightly ahead of the pilot flying. This can include things like changing engine power settings, navigational instruments, flipping through maps and books. While indeed these can be helpful, they will disrupt the flying pilot’s situational awareness when they come as a surprise.
There is a worse problem. If a flight proceeds with a mushy sense of who is in charge of what, there can be aspects where neither pilot is in charge of something important. For example, during a flight this evening, both I and another pilot twice missed a crucial aspect of an instrument approach (timing the final approach leg), which happened partly because we were both reviewing and advising each other about what bits to do next. Neither of us felt in complete charge.
This kind of thing has also happened to me earlier, in flight training. One particularly assertive instructor in the right seat made a habit of supplying continuous corrective advice during challenging portions. Realizing that he was monitoring the situation closer than I could, I no longer felt responsible for the outcome, so I relaxed back to a shrunken level of awareness, making ever more mistakes in a vicious circle. It took many flights to finally put my finger on the problem and put it into words during debriefing. It turned out that we did not fly together much after that.
This sort of problem can be solved by talking about the issue ahead of the flight, and agreeing on a work division scheme, then sticking to it throughout the flight.
One simple scheme I like is having the pilot flying direct the other pilot to do certain specific tasks like “tune this radio to that frequency”, or “find this page in the instrument approach book” or “handle all air traffic radio traffic”, or even just “monitor my performance”. The pilot flying maintains control over the situation by driving (in a literal as well as a figurative sense) the entire progress of the flight. He is in charge of scheduling, making decisions, exercising responsibility. Initiative from the pilot not flying would be restricted to asking “would you like me to do X?”, if doing X soon sounds appropriate.
Another simple scheme is to let the pilot not flying take overall responsibility, treating the pilot flying only as a glorified autopilot. This might be the safest way, since simply keeping the aircraft under positive control can take quite some effort at times. and is of the highest priority. Assigning a person to this task only is likely to ensure that it gets done right.