NTSB investigating Near Miss Between United Jet and small airplane near SFO - ATC Audio

The NTSB emailed a press release about 1 PM PDT today stating “NTSB has launched an investigation to determine why a commercial jetliner and a small light airplane came within an estimated 300 feet of colliding over San Francisco on Saturday.” While much of this event has been made by news media, a review of the San Francisco tower tape shows that both aircraft were in contact with the tower and followed their instructions. Transcripts of the ATC audio suggests that neither aircraft was in danger, though the aircraft may have been a little closer to each other—a loss of separation in FAA parlance—than permitted. Note: I've edited the ATC audio to remove non-relevant communications. [Follow-up article: New NTSB Rules May Increase Reports of Near Mid-Air Collisions].

The rules for separation vary depending upon where an aircraft is located. These aircraft were both operating in the Class B airspace that surrounds San Francisco and other large airports. In Class B airspace, VFR aircraft, such as the light plane, must be separated from jet aircraft by one of the following three criteria:

1. 1 1/2 miles horizontal separation, or

2. 500 feet vertical separation, or

3. Visual separation.

In this case, the controller was relying upon #3 visual separation. Once the rules for visual separation are met, aircraft are allowed to come as close to each other they would like, as long as they do not collide with each other. In this case, whether there was a loss of separation depends upon whether the controller completed the requirements for visual separation before the aircraft came within 500 feet vertically of each other. The NTSB should be able to make this determination after they compare audio transcripts with aircraft radar tracks. 

The instructions for controllers to establish visual separation are as follows:

A pilot sees another aircraft and is instructed to maintain visual separation from the aircraft as follows:

(a) Tell the pilot about the other aircraft including position, direction and, unless it is obvious, the other aircraft's intention.

(b) Obtain acknowledgment from the pilot that the other aircraft is in sight.

(c) Instruct the pilot to maintain visual separation from that aircraft.

(d) Advise the pilot if the radar targets appear likely to converge.

NOTE-

Issue this advisory in conjunction with the instruction to maintain visual separation, or thereafter if the controller subsequently becomes aware that the targets are merging.

(e) If the aircraft are on converging courses, inform the other aircraft of the traffic and that visual separation is being applied.

(f) If the pilot advises he/she has the traffic in sight and will maintain visual separation from it (the pilot must use that entire phrase), the controller need only “approve” the operation instead of restating the instructions.

At San Francisco, the light aircraft was at approximately 1500 feet when the tower controller advised its pilot “70 Echo, Traffic off the departure end climbing out of 500 heavy triple 7.” The light aircraft advised that it had the Boeing 777 in sight and the controller instructed “Maintain visual separation, pass behind that aircraft.” Once that conversation was completed, the controller established visual separation between the aircraft and they were then legally permitted to come as close to each other as they chose. At issue however, will be whether the controller completed his conversation with the light aircraft before it came within 500 feet vertically of the United Boeing 777. If the aircraft were less than 500 feet apart before he completed the conversation establishing visual separation, than he probably had what controllers call “a deal,” an error which led to aircraft coming closer together than permitted. If he completed the conversation in time, than it seems unlikely that any rules were broken.

Note that a 777 typically climbs out at about 2,500 feet per minute. Thus if the controller truly initiated the visual separation instructions when the 777 was at 500 feet, he had 12 seconds to complete the conversation before the aircraft reached 1000 feet. 

So if no rules were broken, why was the event reported? According to the NTSB, the United aircraft’s TCAS unit issued a conflict resolution. This occurs when it detects a potential collision and issues instructions to climb or descend. Any time a conflict resolution is issued, United company rules require the pilot to file a report to the company’s Flight Safety Awareness Program within 24 hours. Those reports are reviewed within a week by company management, the pilot’s union and the NTSB. And that is probably what triggered the current investigation.

I’ve attached my transcript of the audio below. Note that today’s NTSB press release incorrectly stated that the light plane was “an Aeronca 11AC (N9270E),” and this mistake is being repeated in most news reports. According to a pilot I contacted who was familiar with the incident, the light aircraft was actually N9870E, a Cessna 182, which is confirmed by the San Francisco tower audio. I exchanged email with the NTSB public relations department today and they replied that they will notify the NTSB investigator assigned to the case.

In the transcript, SFO tower is the tower controller. UA889 is the Boeing 777 departing San Francisco for Beijing and 9870E is the Cessna 182, which was flying north to south along highway 101.

11:09:28

9870E: San Francisco Tower 9870 Echo 1.6 [indicating he’s at 1,600 feet]

11:09:33

SFO Tower: 8270 Echo San Francisco tower, roger keep Highway 101 off to your left side

11:09:33

9870E:  70 Echo

11:10:03

SFO Tower: United 889 28 Left Heavy Position and hold

11:10:06

UA889:  Position and hold 28 Left, United 889

11:11:41

SFO Tower: United 889 Heavy Winds 090 at 6, Runway 28 Left Clear for takeoff.

11:11:41

UA889:  Clear for takeoff 28 Left United, uh Triple 889

11:13:44

SFO Tower: 70 Echo, Traffic off the departure end climbing out of 500 heavy triple 7.

11:13:49

9870E: 70 Echo is in sight

11:13:51

SFO Tower: Maintain visual separate, pass behind that aircraft

11:13:55

9870E: 70 Echo, Pass behind him

11:13:57

UA889:  Is that Traffic for 889?

11:13:59

SFO Tower: Just ahead and to your right, has you in sight, Cessna one-thousand 500, they’re maintaining visual separation

11:14:05

UA889: [Unintelligible]

11:14:07

SFO Tower: 889 Heavy traffic no factor, Contact Norcal Departure

11:14:10

UA889: OK, That set off a TCAS that was….that

11:14:18

UA889:  We need to talk.

11:14:21

SFO Tower: Roger.

Comments

[Thomas]

I'm not so sure this was simply a "loss of separation". I read the jet pilots' statements that said the Cessna was belly-up to them in a very hard left turn getting away. It sounds like a late ATC attempt to get the VFR traffic to take responsibility AND it seems like the only reason the planes were "only" separated by a few hundred feet was because the jet was leveling off(TCAS) and the Cessna was agressively banking away. I would guess that but for both these actions, the outcome might have been much closer.

[Fernando]

I may be wrong here, but FAA 7110.65J (7-2-1) says that visual separation can only be used if another approved method of separation is assured before and AFTER the application of visual separation. 7-9-4, which refers to separation in Class B airspace also makes reference to 7-2-1. The controller may still be at fault because other approved methods were not assured after the visual separation was applied. I also have to agree with Thomas... the Cessna was in a hard turn to avoid the 777 and from the ATC audio, it sounded as if the United pilot was shaken up a bit. This incident may have turned up worse.

[Max Trescott]

Thomas, I don't know how close the aircraft came either. I agree, it seems highly likely the controller made a late traffic call.

Fernando, I referred to FAA 7110.65J before writing the post. Then I phoned the supervisor's desk at NorCal approach, which handles the SFO Class B, to confirm how they handle visual separation. He told me that once it's established there is no minimum distance required between aircraft. Given his position, I assumed he was correct. If he's not, then we really have a big problem.

[Dave]

Once Visual Separation has been established planes can be INCHES apart,it is the responsibility of the pilot to maintain separation.

[Pathfinder]

Perhaps he was late, but the Cessna did not seem perplexed when acknowledging the avoidance instruction. The United pilot sounded confused even before she took off (goofing the call sign saying triple and not heavy). Hearing how flummoxed she was with a TCSA alarm, I am glad it was not an engine fire alarm. Why don’t we wait until all the data is in before saying the controller made an error?

[Matthew]

The very least they need to investigate it. I know some airline/aviation geeks like me like to get close and video an airliner. There's a 787 landing video online where the guy got pretty close to it while it was coming in. Maybe that pilot in the cessna did the same thing.

Course, then again what the heck is a cessna lurking around the departure end of an airport in Class B? Usually here in KSLC they make you transition above the touchdown zone not the departure end of the runway...I guess San Fran doesn't do that?

They (FAA) probably need to rethink the transitions in and out for VFR aircraft, sort of a north and south transition because there's no way no reason a VFR/IFR Cessna should be in the path of the departure end of a runway. That's my .02

[Winstonc]

It seems probably material to note that in addition to the reporting requirements of the United company rules, an immediate incident notification is also required to be made directly to the NTSB, per the 3/8/10 revisions of NTSB 830.5, whenever the ACAS issues a conflict resolution, as it seems to have happened here. Really enjoy the blog - keep it up!

[Max Trescott]

Pathfinder, I agree the United Captain did flub her callsign on takeoff, though I attribute that to pilots having multiple callsigns a day--I don't think that's uncommon. She's clearly upset later. I don't think I said the "controller made an error," though with what data there is it seems plausible. Given that both pilots followed all instructions, it's not obvious how they may have been at fault other than a general catch-all such as 91.13 Careless or Reckless Operation.
Matthew, the Cessna wasn't lurking.I don't believe it's hazardous to fly along Hwy 101 as the Cessna was doing. Probably a 100 planes a day do that and I'm not aware of any prior conflicts. Most departures are off Rwy 1L and 1R and arrivals are on 28L and 28R, none of which conflict with 101 transitions. When they do occasionally launch a heavy off 28L or 28R, they usually tell the small planes to turn to a heading of 280, to parallel the departure aircraft, or to cross overhead the field. Both work fine, though neither was used in this case.
Winstonc, you make a great point. I wonder if the new NTSB 830 rule will lead to many more of these kinds of notifications. If they do, we're going to see a lot of these stories in the press, at least until they figure out that trying to pedal these stories every day doesn't increase their ratings. Of course if it does....

[Alan]

As long as the controller isn't required to use any method other than visual seperation, I think the pilot of the 182 is at most fault. He confirmed that he had a visual of the 777 and that he would maintain visual seperation. Assuming he never lost sight of the departing 777, why did he let himself get close enough to have to make a hard banking turn to avoid colliding with it?

[Max Trescott]

Alan, No question, the C182 pilot could probably have done more sooner to avoid the B777. However, he followed every instruction he was given. The controller is required to keep the aircraft apart at least 500 feet vertically and 1.5 miles horizontally. If he uses visual separation, the aircraft have to stay that far apart until he completes the communications with the aircraft that result in establishing visual separation. The planes may have been closer to that when the controller issued the instructions establishing visual separation.

[John P]

As a 3000 hour Mooney pilot, I will acknowledge that it can still be difficult to judge the speed and path of another aircraft when told to maintain visual separation. Particularly large planes appear to be flying slower than they are (it's a real, visual miscue... it's why big ships look like they're going slowly when doing 30 knots), so it's possible the Cessna pilot thought all was well for a few seconds before realizing a potential danger.

[pinot4me]

If the timeline above is correct it appears that two minutes elapsed between the takeoff clearance and the call that the 777 was out of 500.

[Nick]

She may have flubbed the callsign, but that `aint a prob, she asked ATC IF that was her traffic - she also said that shae had a TCAS - given that both pilots especially the Cessna were fully aware of each other then it was SAFE visual seperation - and, of course, at that proxi it would indeed set the TCAS for a TA (which should not really be an RA for that stage now should it?!?!?! - no, quite. So, El Capitaina of the triple 7 heavy has 1/. Not been sure if her traffic was HER traffic due to her call. 2/. Has responded to a TCAS when it was the only instance where you would not. 3/. She was obviously holding it all together but not quite - she may have been in the mindset that all would be laid out for her Heavy departure - not the case. She had traffic so she would have to be aware of that traffic in every pictorial way possible - she should have then continued - as she was airborne already - and flown tactically, there would be no time to go comms with ATC she should just have flown very visually indeed, if she was not sure of HER traffic.
All of the above is deleted if the Cessna traffic, were NOT visual, or they were so lax as to make there passing behind too late or were simply not paying attention. If, if, the Cessna was indeed filling up her windowscreen with its belly then this is fault of the Cessna - who should have known better and taken action sooner, like when the ATC told him to pass behind the 777 - ATC could have vectored the Cessna out of the way of the triple - but to have a Cessna pass behind a Heavy triple is folly anyway due to wake turbulence - all in all; The ATC should have held the triple 7. This would have given Mrs. Captain time to be super ready. This would have enabled ATC to get rid off the Cessna. The Cessna pilot would have appreciated the need for a vector out of there. There would then have been less risk of any wake vortex for the Cessna.
Job done. Instead of rushy, rushy, rushy.

[Nick]

ATC should have held the heavy at the threshold. ATC shouold have given the Cessna immediate vectors away from the proposed flight path of the heavy. This would have given time for the Captain to settle in before departure. This would have avoided the Cessna having to pass behind a triple 7 risking vortex. (big time) This would have prevented Mrs. Captain from going 2 way with ATC asking confirmation of her traffic when she should have been flying tactically. Hindsight is an easy thing. "Hold position would have been fabulous. Mrs. Captain was not ready for THIS. Mr. Cessna was slow. Mr. ATC assumed both pilots would visually seperate. TCAS caused a stir which in this situation TCAS should be TA any way - so if TCAS was RA - the triple would be jumping about all over the place at 500 and in an obvious area of intense traffic.