Cresson helpers question

Please bear with me for what is possibly a silly question , but I'm not familiar with operations over in the US.

I'm interested in NS's helper operations based on Cresson , more specifically where do they get attached and detached from the trains - one website says that they go on the train at Altoona heading towards Cresson , but doesn't say where they come off, whilst another implies that they come off at Cresson itself.

I know that the SD50Es used have the Helperlink system fitted so that they can uncouple on the move , but where does this happen?

Thanks in advance

Rich

Westbound helpers are added in Altoona. Depending on the train, some helpers cut off in Cresson while others run all the way to Johnstown. A few trains keep helpers all the way to Pittsburgh. Eastbounds can get helpers in Pittsburgh, Johnstown or Cresson and are cut off in Altoona.

Trains can also get helpers on or off at ConPit.. Helpers that go to Pittsburgh on westbound trains will return on east bounds (coal trains) to help over the grade at Greensburg, PA. No coal train going east or west can go over the mtns without helpers at both areas.
Cresson is where Head-End helpers are put on if the crew of the train has run out of time.
But all depends on the train & what dispatch can do.

Why helpers (a/k/a "Snappers")?

MP 275 (Johnstown) to MP 263 (Summerhill) - 12 miles - 0.63% uphill grade
MP 263 (Summerhill) to MP 260 (Flynn's Curve) - 3 miles - 0.4% uphill grade
MP 260 (Flynn's Curve) to MP 249 (Helman's Curve, Gallitzin) - 11 miles 1.05% uphill grade
MP 249 (Helman's Curve, Gallitzin) to Gallitzin Tunnel West Portal - 1/3 mile - 0.74% uphill grade
Gallitzin Tunnel West Portal to East Portal - 3/4 mile - 1.21& downhill grade
MP 247 (east of East Portal) to approx. 2/3 mile east - 2.27% downhill grade
MP 247ish to MP 242 (Horseshoe Curve) - 5 miles - 1.76/1.77% downhill grades
Through Horseshoe Curve - 1/4 mile - 0.34% downhill grade
MP 242ish to MP 237ish (Alto Tower) - 3 miles - 1.82/1.45/1.85/1.12/1.51% downhill grades

Going eastward it's a long, momentum-sapping drag, followed by a make-sure-the-brakes-work run into Altoona.
Going westward it's an I-think-I-can-I-think-I-can uphill battle, followed by let's-coast-downhill-without-losing-control.