Hello, all. In summertime here in Florida, garden variety storms are a daily thing. And, with my limited knowledge of airmanship, I gather they are to be avoided at all cost. So, when an A319 from Miami to Tampa has to make a swing over the Gulf that seems almost half the total original flight distance to dodge a buildup, whose call is that? Pilot? ATC? Airline dispatcher? A combination? In watching flight trackers, I've figured that enroute dodging seems much more open ended than in a terminal area with arrivals and departures lining up pretty similarly to go around a big red cell. Thanks.

Combination. But ultimately the flight commander makes the final decision (as it is and as it should be).

Weather is closely paid attention to by flight dispatchers and they will plan fuel loading based on expected weather and hence routing at the time of departure. Then the final say from aircraft commander. It’s a science… but not exact in its outcomes. A storm can “sit” over or near the airfield, stopping flights, and cause more problems than just having to re-route for weather.

As you note, the terminal area is fixed in position, en-route has more possibilities with avoiding weather. But things can and do change rapidly and this is where the computer models and also the experience of dispatchers, ATC and pilots really get to show their worth.

It’s a huge team effort with the Captain making the final decision.

"Avoided at all costs" is not quite true. You can often fly through the "green" areas at the edges of cells without issues beyond turbulence.

Certainly. you don't want to fly into the middle of a cell, but often you have no choice but to fly through a line of storms by threading between cells. In the terminal area, you can't just deviate by twenty miles, so you'll accept the bumps. Everyone is seated already so you're not disrupting the service or anything.

Wind direction is a big factor in avoidance. Even relatively near a cell, you might feel nothing if you are upwind.

As a retired TRACON controller and 1,500+ hour Private Pilot I'll offer this. The newest software and displays we had probably back in 2009ish offered us ATC kids a huge advantage in having weather available to us in the operation with color displays. We finally got to see almost what the pilot was seeing, though a visual out of the windscreen on the flight deck was always the best look at what was happening regarding weather and storms.

My philosophy that I adopted from flying was let the pilot tell you what they see and allow me as a controller to offer suggestions from where I see the storms moving since I am sitting stationary and the pilots are moving. I'd offer a suggestion of which was to go and if they verified it then let them fly that route, when finished deviating give them a fix or heading to follow on with from that point. I'd always ask the crew for a ride report to pass along to those following and of course as the storms would move we'd have to adjust the route of the following arrivals/departures.

As controllers we could not detect a cloud that was building, only those in the sky could and as a result at times we'd put the aircraft right through the top of something growing. That's when it was a huge help for the pilots to tell us what was happening before we started to see the precipitation on our displays. It's a total team effort from Ground Control right through to Ground Control with all aspects working to give a safe flight to all.

IAHFLYR wrote:

I'd offer a suggestion of which was to go and if they verified it then let them fly that route, when finished deviating give them a fix or heading to follow on with from that point. I'd always ask the crew for a ride report to pass along to those following and of course as the storms would move we'd have to adjust the route of the following arrivals/departures.

As a dispatcher this is very close to my approach as well. Often what I can see is more helpful to give trends, movement and what's is behind the near cells, as the onboard Radar will not do well to paint behind an intense area.
Nothing however annoys me like the Sermn routes out of EWR. they always seem to be required whilst flying 8000ft right into a squall line.

Starlionblue mentions that you must sometimes thread your way through thunderstorm cells. The question I have is maybe slightly off topic, but I've always wondered how you can deviate from a set course, thread your way through thunderstorms, and then return to your original course of travel. Is it like the route guidance in a vehicle that continually updates your position if you deviate from the original course? Or, does the flight crew and ATC have to recalculate where the plane is and what needs to be done go to get back on course? As anyone can tell, I'm not a pilot (A&P mechanic for FedEx), yet have a keen interest in how all things aviation works.
Gregory

gregorygoodwin wrote:

Starlionblue mentions that you must sometimes thread your way through thunderstorm cells. The question I have is maybe slightly off topic, but I've always wondered how you can deviate from a set course, thread your way through thunderstorms, and then return to your original course of travel. Is it like the route guidance in a vehicle that continually updates your position if you deviate from the original course? Or, does the flight crew and ATC have to recalculate where the plane is and what needs to be done go to get back on course? As anyone can tell, I'm not a pilot (A&P mechanic for FedEx), yet have a keen interest in how all things aviation works.
Gregory

From what I have seen in YouTube videos, pilot requests a deviation, ATC gives them deviation, and they can do what they need to do. They might request to deviate 40 miles left of track, for instance. You would be using heading select at that point. To get back on track would also require ATC coordination.

gregorygoodwin wrote:

Starlionblue mentions that you must sometimes thread your way through thunderstorm cells. The question I have is maybe slightly off topic, but I've always wondered how you can deviate from a set course, thread your way through thunderstorms, and then return to your original course of travel. Is it like the route guidance in a vehicle that continually updates your position if you deviate from the original course? Or, does the flight crew and ATC have to recalculate where the plane is and what needs to be done go to get back on course? As anyone can tell, I'm not a pilot (A&P mechanic for FedEx), yet have a keen interest in how all things aviation works.
Gregory

When you deviate, the course line will still be displayed in dashes. You'll be in heading mode or paralleling using an offset.

Once it is time to get back on track, ATC will ask you to either go direct from present position to the next waypoint, or rejoin the course. On Airbus, if you're in HDG mode and your heading will bring you towards the course line, you can push the heading know to arm NAV mode. The system will calculate, display, and execute an intercept, at which point NAV will activate.

Except the in the photo above, it doesn’t make any sense as there is no valid NAV intercept, and so the FMA shouldn’t annunciate NAV armed to capture the lateral path.


When in a radar environment, ATC can see where aircraft are and pilots ask for a left/right deviation.

I usually ask for a left/right, an angle (10-20-30 degrees) and a distance. (60 miles/75 miles.)

Enroute/center controllers usually grant the deviation unless something prevents it like airspace or conflicting traffic and also give an enroute fix that is on the flight plan to end the deviation. After we have maneuvered around the weather, we just DIR TO the fix that the controller has assigned and we report that we are proceeding DIRECT.

If things just get too congested on the radio, and I can’t get a word on the radio to ask for a deviation, I just state on the radio, “XYZ flight 1234 is deviating left/right 30 degrees for weather.” And let the controller sort it out.


There was one time, an aircraft was flying over the Grand Canyon, and the pilots asked the controller for S-turns so they could give their passengers a view of the Grand Canyon. The controller said that he couldn’t authorize a deviation for sightseeing… The pilots sounded disappointed. Then the controller told the flight, “Left and Right deviations for weather approved, Twenty-Nine Palms when able.” So at that point, the pilots are able to turn left or right as the pilots see fit, and then when they were done, they just push the DIR TO button, and select TNP and execute.

Woodreau wrote:

Except the in the photo above, it doesn’t make any sense as there is no valid NAV intercept, and so the FMA shouldn’t annunciate NAV armed to capture the lateral path.

Well spotted. I gave up looking for a more accurate image after a few minutes of googling.

Woodreau wrote:

Except the in the photo above, it doesn’t make any sense as there is no valid NAV intercept, and so the FMA shouldn’t annunciate NAV armed to capture the lateral path.

Does it have to intercept the same leg you came out of? In other words if the route turns left beyond the range of the ND (which is only 10 nmi anyway) would that then make it a valid intercept?

N47 wrote:

Woodreau wrote:

Except the in the photo above, it doesn’t make any sense as there is no valid NAV intercept, and so the FMA shouldn’t annunciate NAV armed to capture the lateral path.

Does it have to intercept the same leg you came out of? In other words if the route turns left beyond the range of the ND (which is only 10 nmi anyway) would that then make it a valid intercept?

If vague memory serves it has to intercept before the next waypoint after the current "TO waypoint" (DIBAG).

I think you may be making this too complicated. When you deviate you will ask for a "x" number of degrees turn or "x" number of miles L or R. When you're ready to resume your course ATC may give you direct to a point down the road or a heading or turn to intercept your course.

CosmicCruiser wrote:

I think you may be making this too complicated. When you deviate you will ask for a "x" number of degrees turn or "x" number of miles L or R. When you're ready to resume your course ATC may give you direct to a point down the road or a heading or turn to intercept your course.

Indeed.

Typically we'll ask fo a "x miles" deviation off track when en route, and "x degrees" when in the terminal area.

We usually just said we need a 20 deg left turn for weather though the offset would certainly be a good choice too. . I rarely did offset track except over the Atlantic.

CosmicCruiser wrote:

I think you may be making this too complicated. When you deviate you will ask for a "x" number of degrees turn or "x" number of miles L or R. When you're ready to resume your course ATC may give you direct to a point down the road or a heading or turn to intercept your course.

Exactly, not very difficult at all though some controllers make it difficult just because that is who they are.....simply put they are not comfortable with going away from the facility procedures during weather events.

CosmicCruiser wrote:

We usually just said we need a 20 deg left turn for weather though the offset would certainly be a good choice too. . I rarely did offset track except over the Atlantic.

Understood.

As I see it, turns in degrees work well in a radar environment. However, a lot of our storm deviation en route seems to be in non-radar environments in the ITCZ. The controller can't see us and there may be storms for hundreds of miles.

If we ask for, say, "up to thirty miles left of track", this allows us to roam free between the track and thirty miles left of it. With complex and extensive storm systems, we may not know exactly how we need to turn in ten minutes, and then ten minutes after that. Simpler to ask for one deviation with flexibility than to keep asking for new tracks which the controller can't see anyway.

Very true. A lot of our deviations were in non radar environments and looking and tracking the storm on our radar we would pick a good heading and ask for the turn. I see your point too. Worst case scenario was those times that when not only were you not in radar contact but you couldn't raise anyone on the radio. Just a call in the blind of what we were doing. Sending you a PM